Construction materials and structures proceedings (pg 225 469)

S Hong et al / Study on Drying Shrinkage Cracking Characteristics of SCRPCC 201 Ωcd : free drying shrinkage strain of outdoor specimen Overall, average crack width of restrained specimens was decreased by increasing of the amount of reinforcing bar In the case of specimens with low reinforcement ratio (PCM4, SCP4), average crack width of PCM specimen was decreased by reinforcing with steel chip And average crack width of specimens with high reinforcement ratio (PCM10, SCP10) was that PCM specimen was lower than SCP specimen Figure Relationship between average crack width and drying period Conclusions Copyright © 2014 IOS Press All rights reserved In this paper, the drying shrinkage properties and the cracking characteristics of the newly developed SCRPCC with large scale wall specimen were investigated The following conclusions can be obtained (1) Drying shrinkage of all free shrinkage specimens increased with drying period And the drying shrinkage was decreased by reinforcing with steel chip at the outdoor condition Influence of curing and drying condition on drying shrinkage is that drying shrinkage of outdoor specimens was lower than that of indoor specimens (2) Drying shrinkage of restrained PCM specimens was reduced by reinforcing with steel chip And in the case of specimens with high reinforcement ratio, the occurrence of cracks of restrained SCRPCC specimen was less than that of PCM specimen (3) Average crack width of restrained specimens was decreased by increasing of the amount of reinforcing bar And in the case of specimens with low reinforcement ratio, average crack width of PCM specimen was declined by reinforcing with steel chip References [1] T Wakatsuki et al., Development of Fe-Mn-Si- Cr Shape Memory Alloy Machining Chips Reinforced Smart Composite, Journal of the Iron and Steel Institute of Japan 92(2006), 562-566 (in Japanese) [2] R.N Swamy and H Stavrides, Influence of Fiber Reinforcement on Restrained Shrinkage and Cracking, ACI Journal, 76(1979), 443-460 [3] S Hong, Experimental Study on Drying Shrinkage Cracking Characteristics of Steel Chip Reinforced Cementitious Composite, the Proceeding of JCI, 35(2013), 601-606 [4] Y Ohama, Principle of Latex Modification and Some Typical Properties of Latex-Modified Mortars and Concretes, ACI Materials Journal, 84(1987), 511-518 [5] M Koyanagi, Y Masuo and S Nakane, A Study on Shrinkage Cracks in Reinforced Concrete Walls (Part 4) Prediction Analysis of Cracking Widths due to Restrained Volume Change in One-Way Concrete Members”, Report of Obayashi Corporation Technical Research Institute, 41(1990), 73-79 (in Japanese) [6] G.F Kheder, A New Look at the Control of Volume Change Cracking of Base-Restrained Concrete Walls, ACI Structural Journal, 94(1997), 262-270 Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 202 Construction Materials and Structures S.O Ekolu et al (Eds.) IOS Press, 2014 © 2014 The authors and IOS Press All rights reserved doi:10.3233/978-1-61499-466-4-202 The effect of steel and polypropylene fibres in the mechanical properties of structural lightweight concrete S P YAP, Ubagaram Johnson ALENGARAM1, and Mohd Zamin JUMAAT Department of Civil Engineering, University of Malaya, Kuala Lumpur Abstract The effect of fibres in the structural lightweight concrete made from palm kernel shell (PKS) as coarse aggregate and to enhance the mechanical properties of palm kernel shell concrete (PKSC) was investigated The crushed PKS was used to replace the conventional crushed granite wholly and thus it falls under the category of sustainable construction; the use of PKSC as the structural lightweight concrete could lead to a reduction in the construction cost and also environmentally beneficial as PKS causes land pollution In this paper, steel fibres of aspect ratio 65 and fibrillated polypropylene (PP) fibres were added in the PKSC The compressive and flexural strengths of palm kernel shell fibrereinforced concrete (PKSFRC) were evaluated The experimental results show that steel fibres produced significant improvement on the mechanical properties of PKSFRC The enhancement on compressive and flexural strength are 23% and 27%, respectively higher than control mix However, the compressive strength and the tensile strength increment in PKSFRC containing PP fibres was lower than the steel fibres In addition, the addition of fibres in PKSFRC reduced the brittleness of the PKSC significantly Hence the role of fibres in enhancing the mechanical properties and brittleness of PKSC is evident Keywords Polypropylene fibres, mechanical property, lightweight concrete Copyright © 2014 IOS Press All rights reserved Introduction The researches on the utilization of palm kernel shell (PKS) as lightweight aggregates to produce lightweight concrete (LWC) has been reported for few decades (Alengaram et al 2013) PKS is a waste material from the palm oil industry which generated after the extraction of palm oil from the palm oil fruits (Fig 1) As the second largest palm oil production country, Malaysia produced 2.4 million tons of PKS as waste (MPOB, 2011) and these wastes are generally dumped in open air This eventually results in environmental pollutions such as contamination of underground water and soil, as well as increased costs to manage the waste Therefore the application of PKS as coarse aggregate to replace the rapid depleting granite aggregates paves way to produce a more sustainable concrete Corresponding author: Faculty of Engineering, University of Malaya 50603, Kuala Lumpur, Malaysia; Email johnson@um.edu.my Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 S.P Yap et al / The Effect of Steel and Polypropylene Fibres in the Mechanical Properties 203 Figure Palm Oil Fruits (left) and PKS (right) Copyright © 2014 IOS Press All rights reserved In addition to the environmental benefits, the lightweight characteristic of PKS enables the production of LWC The use of LWC in the construction industry enables the dead load reduction on buildings and this eventually allows for greater design flexibility and cost savings on structural members and foundation construction (Yap et al 2013) The early published researches on OKS reported that LWC called PKS concrete (PKSC) with a density and compressive strength in the range of 1700-1850 kg/m3 and 5-25 MPa, respectively (Basri et al 1999; Mannan & Ganapathy 2002) could be produced with 100% coarse aggregate replacement by PKS However the low mechanical properties, especially the compressive and tensile strengths, and high brittleness of LWC including PKSC compared to the normal concrete have held the development of PKSC in the structural applications (Domagala 2011) One of the methods to improve the mechanical properties of the PKSC is by the inclusion of fibres as the construction industry is now aware of the benefits of fibers in enhancing the concrete properties The main advantages of fibres in concrete are enhanced flexural capacity, toughness, ductility, crack control, impact strength and others (Hassanpour et al 2012) In this study, two different fibres, steel and polypropylene (PP) fibers were added into PKSC to produce PKS fibre-reinforced concrete (PKSFRC) This paper aims to improve the mechanical properties of the PKSFRC to meet the structural requirements of the LWC to widen the applications of PKSC This study serves as a preliminary research on future evaluation of other properties of PKSFRC Materials and methods 1.1 Materials 1.1.1 Cement & supplementary cementitious material Ordinary Portland Cement (OPC) with a Blaine specific surface area and specific gravity of 335 m2/kg and 3.10, respectively and 10% (of cement weight) silica fume were used in all the mixes Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 204 S.P Yap et al / The Effect of Steel and Polypropylene Fibres in the Mechanical Properties 1.1.2 Coarse aggregate PKS were collected from the local crude palm oil mill (Fig 1) The PKS was sieved using a mm sieve and the OPS retained on the mm sieve were crushed to obtain the PKS with maximum size of mm The physical properties of PKS are shown in Table It should be noted that the effect of high water absorption of PKS (Table 1) was compensated by using PKS in saturated surface dry condition during the mixing Table Comparison of physical properties between PKS and crushed granite Physical properties OPS Compacted bulk density, kg/m3 Specific gravity 24-hours water absorption, % Aggregate Impact Value (AIV), % 658 1.35 19.1 2.63 Crushed granite (Mannan & Ganapathy 2002) 1470 2.61 0.76 17.29 1.1.3 Fine aggregate Mining sand was used as fine aggregate with the specific gravity and fineness modulus of mining sand were found to be 2.65 and 2.71, respectively 1.1.4 Water and superplasticizer Potable water with a pH value of 6.4 was used for all mixes A polycarboxylate-based superplasticizer was used in all mixes to improve the workability of the mixes 1.1.5 Fibers Two types of fibers were added into OPSC: (i) steel fiber and (ii) PP fibers The basic properties of the fibers are displayed in Table Copyright © 2014 IOS Press All rights reserved Table Properties of steel and polypropylene (PP) fibers Fiber Geometry Length (mm) Diameter Specific gravity Tensile strength (MPa) Steel Hooked-end 35 0.55 mm 7.90 1100 PP Fibrillated 19 1000 denier 0.90 400 1.2 Mix proportions A total of mix proportions were prepared (Table 3) All the constituent materials were kept constant while the differences between the mixes are the type of fibers A fiber content of 0.5% (of concrete volume) was used in the PKSFRC mixes Table Mix proportions Mix Description PKSC PKSFRC-ST PKSFRC-PP Control 0.5% steel fiber 0.5% PP fiber Constituent Materials (kg/m3) OPS Sand Cement Water 335 980 500 160 Fiber (%vol.) Steel PP 0 0.5% 0 0.5% Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 205 S.P Yap et al / The Effect of Steel and Polypropylene Fibres in the Mechanical Properties 1.3 Specimen preparation and testing procedures The workability (slump) of all mixes was measured in accordance to the ASTM C143 (2010) For each mix, fifteen 100 mm cubes and three 100 x 100 x 500 mm prisms were prepared to be tested for corresponding testing: compressive strength (BS EN 12390-3, 2000) and flexural strength (ASTM C78) respectively After the de-moulding, all the specimens were cured in water and all of the samples were tested the age of 28day except the cubes The cubes were tested at the age of 1-, 3-, 7-, 28- and 56-day Results and discussions 2.1 Slump The addition of fibers into concrete generally causes significant loss in concrete workability, attributed to larger surface area of fibers than aggregates which results in the requirement of more cement paste to wrap around the fibres (Chen and Liu 2005) From Table 4, PKSFRC-PP produced the lowest slump; It produced 50% slump reduction relative to the control mix However, the PKSFRC-ST produced a slump value of 40 mm with 33% slump reduction The difference between the slump values of the steel and PP fibers is due to the larger surface area in PP fibers which requires a huge amount of cement paste to wrap around to form the fibre-matrix interfacial bonding, eventually reduced the flow ability of the fresh cement matrix Despite the low slump values, all three mixes attained good compaction and finishing 2.2 Oven-dry density Copyright © 2014 IOS Press All rights reserved The EN 206-1 defined lightweight concrete (LWC) as concrete having an oven-dry density (ODD) of not less than 800 kg/m3 and not more than 2000 kg/m3 which is produced using lightweight aggregate for all or part of the total aggregate Hence all the PKSC and PKSFRC mixes from Table fulfilled the requirement to be considered as LWC with the ODD within the range of 1725-1810 kg/m3 The PKSFRC-ST showed higher ODD than other two mixes, due to the high specific gravity of steel fibres of about Table Mechanical properties of OPSC and OPSFRC Mix PKSC PKSFRC-ST PKSFRC-PP Slump (mm) 60 40 30 Oven-dry density (kg/m3) Compressive strength (MPa) 13728day day day day 1725 18.6 29.3 30.3 31.6 1810 23.6 29.1 35.9 38.8 1740 20.9 28.2 31.8 33.8 * brittleness = compressive to flexural strengths ratio Flexural strength (MPa) Brittleness* 4.74 6.03 5.15 7.3 6.4 6.6 2.3 Compressive strength The compressive strengths at the age of 1-, 3-, 7- and 28-day are reported in Table The control mix produced 28-day compressive strength of 32 MPa, while the PKSFRC Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 206 S.P Yap et al / The Effect of Steel and Polypropylene Fibres in the Mechanical Properties reinforced with steel fibers showed the highest compressive strength of about 39 MPa, which was 23% higher than control concrete Further, PKSFRC-PP showed slight improvement of compressive strength The beneficial effect of fibers on enhancing compressive strength of concrete is mainly due to the crack bridging effect Under an increasing compression loading, cracks will initiate and advance When the advancing crack approaches a fiber, the debonding at the fiber-matrix interface begins due to the tensile stresses perpendicular to the expected path of the advancing crack As the advancing crack reaches the interface, the crack tip stress concentration is reduced and thus the propagation of crack is blunted and blocked (Yap et al 2013) In the crack bridging, the additional stress taken by the fibers is governed by the tensile strength of the fibers Steel fibers possess high tensile strength and hence it provided high improvement on the compressive strength of PKSC While marginal effect of PP fibers on compressive strength of PKSC might due to the low stiffness of PP fibres which resulted in less crack bridging effect to be induced in the fibre-matrix network Other than that all the mixes achieved high early strength (Table 4) At the age of 3-day and 7-day, the mixes produced 70-90% and 80-95%, respectively of their corresponding 28-day compressive strength The high early strength of OPSC is the high reactivity and micro filler effects of silica fume added into OPSC (Yap et al 2013) 2.4 Flexural strength Copyright © 2014 IOS Press All rights reserved The flexural strengths were investigated and shown in Table However the low tensile strength in PKSC arises the use of fibres in PKSC In this study, the control mix without any fibers produced 4.7 MPa in the flexural strengths In comparison to the PP fibres, steel fibers produced the highest flexural strength of MPa and it was found 27% higher than the PKSC mix The tensile strengths enhancement is significant However the improvement of flexural strengths in PKSFRC-PP mix was only 9% Judging for the smaller beneficial effects of PP fibers compared to steel fibers, the situation might be attributed to the lower tensile strength of PP fibers This caused a smaller tensile stress taken by PP fibers during crack bridging, compared to the steel fibers 2.5 Brittleness The high brittleness is also another concrete of LWC and PKSC In this study, the brittleness is taken as the ratio of compressive to flexural strengths (Sun & Xu, 2009) A high brittleness ratio indicates that the concrete material fractures and loses the load bearing capacity under tensile stress at a much lower loading, compared to the compressive strength Based on results from Table 4, the control mix produced a brittleness ratio of about 7.3, while the PKSFRC reduced the brittleness significantly to 6.4-6.6 The presence of fibres in the cement matrix contributes a restraining effect on the matrix and this eventually allows the concrete to sustain higher deflection after the cracking commences The crack bridging effect also aids in holding the concrete together Therefore the inclusion of both steel and PP fibres significantly reduced the brittleness of PKSFRC Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 S.P Yap et al / The Effect of Steel and Polypropylene Fibres in the Mechanical Properties 207 Conclusions The following conclusions could be drawn: x Addition of fibers into the PKSFRC significantly reduced the slump x Both PKSC and PKSFRC fulfilled the requirement of LWC with oven-dry density 1725-1810 kg/m3 The addition of 0.5% steel fibers increased the dry density by 5% but PP fibers have negligible effect on dry density of OPSC x Steel PKSFRC experienced significant enhancements of both the compressive and tensile strengths of PKSC x PP fibers slightly improved on compressive and flexural strengths of PKSC, with only marginal enhancement of about 9% on the flexural strength of PKSC x The addition of both steel and PP fibres reduced the brittleness of PKSC x The use of steel fibers is highly recommended to enhance the mechanical properties of PKSC Acknowledgement The authors are grateful to University of Malaya for the financial support through the University of Malaya Research Project RP018-2012B: Development of geo-polymer concrete for structural application References Copyright © 2014 IOS Press All rights reserved [1] Alengaram, U J., Al Muhit, B A., and Jumaat, M Z 2013 Utilization of oil palm kernel shell as lightweight aggregate in concrete – A review, Construction and Building Materials, 38: 161-172 [2] ASTM C78 Standard test method for flexural strength of concrete (using simple beam with third-point loading) American Society for Testing and Materials (ASTM), 2002 [3] Basri, H B., Mannan, M A., and Zain, M F M 1999 Concrete using waste oil palm shells as aggregate Cement and Concrete Research, 29: 619-622 [4] BS EN 12390: Part Testing hardened concrete- Compressive strength of test specimens British Standard Institution, 2000 [5] Chen, B and Liu J 2005 Contribution of hybrid fibers on the properties of the high-strength lightweight concrete having good workability Cement and Concrete Research, 35: 913-917 [6] Domagala, L 2011 Modification of properties of structural lightweight concrete with steel fibres Journal of Civil Engineering and Management, 17(1): 36-44 [7] Hassanpour M., Shafigh P and Mahmud H 2012 Lightweight aggregate concrete fiber reinforcement – A review Construction and Building Materials, 37: 452-461 [8] Mannan, M A.; Ganapathy, C 2002 Engineering properties of concrete with oil palm shell as coarse aggregate Construction and Building Materials, 16: 29-34 [9] MPOB, Malaysia Palm Oil Board (2011) Production of Palm Kernel and Palm Kernel Cake Website: http://econ.mpob.gov.my/economy/ei_monproduction.htm [10] Sun, Z and Xu, Q 2009 Microscopic, physical and mechanical analysis of polypropylene fiber reinforced concrete Materials Science and Engineering A, 527: 198-204 [11] Yap, S P., Alengaram, U J & Zamin, M Z 2013 Enhancement of mechanical properties in polypropylene– and nylon–fibre reinforced oil palm shell concrete Materials and Design, 49: 10341041 Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 208 Construction Materials and Structures S.O Ekolu et al (Eds.) IOS Press, 2014 © 2014 The authors and IOS Press All rights reserved doi:10.3233/978-1-61499-466-4-208 Utilization of ceramic wastes as replacement of portland cements Viviana RAHHALa,1 Edgardo IRASSARa, Cristina CASTELLANOa Zbyšek PAVLÍKb and Robert ČERNÝb a Departamento de Ingeniería Civil Facultad de Ingeniería UNCPBA, Argentina b Faculty of Civil Engineering, Czech Tech Univ in Prague, Czech Republic Abstract The possible applicability of ceramic waste as partial replacement of Portland cement was studied For this purpose, two ceramic wastes and two Portland cements of different countries (Argentine and Czech Republic) were analysed After characterization of the materials used (chemical and mineralogical composition and specific surface), the effect of ceramic waste replacement (8, 16, 24, 32 and 40 % by mass) was analyzed The pozzolanic activity, the heat released rate and the hydration products were determined at 2, and 28 days Results show that ceramic wastes have pozzolanic activity with both portland cements At early age, the dilution effect governs the properties and finally the pozzolanic reaction improves the performance of blended cements Keywords Portland cement, ceramic waste, heat of hydration, XRD-ray Copyright © 2014 IOS Press All rights reserved Introduction In the cement industry, the manufacture of one ton of portland clinker requires 1.7 tons of raw materials that causes a large consumption of non-renewable mineral resources and a serious depletion of quarrying areas Furthermore, the high temperature process requires high energy consumption and also releases a large volume of CO2 to the atmosphere as a result of decarbonation of limestone in the furnace and the combustion of fossil fuels [1] Additionally, the growth of industrials activity also produced a large volume of solid waste that annually increases in several industrial sectors, becoming an environmental issue add its final deposition Among this industrial sector, the ceramic brick industry growths due to its high heat-efficient envelop for building In Europe, the amount of wastes from different production stages of the ceramic industry reaches to 3-7 % of its global production, meaning millions of tons of calcined-clays per year [2] The same values of scrap are reported for the Latin-American ceramic industry The cement production companies have begun to implement a series of measures to reduce their environmental impact and transform the portland cement into a material with sustainable development In order to find economic, technological and solutions primarily friendlier to the environment, there has been widespread use of industrial byproducts or waste material [3-4], during the manufacture of portland cement In this Corresponding author: Av del Valle 5737 (B7400JWI) Olavarría; Email vrahhal@fio.unicen.edu.ar Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 V Rahhal et al / Utilization of Ceramic Wastes as Replacement of Portland Cements 209 paper the potential of using ceramic wastes as partial replacement of portland cement is studied Materials and methodology Two portland cements (ArgPC and CzPC) and two ceramic wastes (ArgCW and CzCW) were used Portland cements meet the composition of CEM I according to EN197:1 and ceramic wastes come from a red brick factor were they are calcined at about 850-1050ºC The ArgCW is the scrap and it was crushed and ground in a ball grinding mill The CzCW is the ceramic dust obtained after the grinding treatment made on the face of the bricks to calibrate its heights. The characteristics of all materials, chemical and mineralogical composition, density and specific surface (Blaine) are given in Table The chemical composition was determined by X-ray fluorescence and the mineralogical composition of cements was calculated by Bogue´s formulate and the main crystalline minerals of ceramic waste was determined by XRD Table Characteristic of materials Parameters Copyright © 2014 IOS Press All rights reserved SiO2, % Al2O3, % Fe2O3, % CaO, % MgO, % SO3, % Na2O, % K2O, % TiO2, % Loss on ignition Density SS Blaine, m2/kg C3S, % C2S, % C3A, % C4AF, % Gypsum, % Portland Cements ArgPC CzPC 21.5 18.9 3.8 4.2 3.8 3.8 64.3 62.4 0.8 1.0 2.6 2.3 0.1 0.0 1.1 0.0 0.8 2.1 1.5 3.15 3.10 315 330 60.0 50.5 16.4 19.2 3.8 8.8 11.5 11.6 5.5 7.2 Parameters SiO2, % Al2O3, % Fe2O3, % CaO, % MgO, % SO3, % Na2O, % K2O, % TiO2, % Loss on ignition Density SS Blaine, m2/kg Mineralogical composition Ceramic Wastes ArgCW CzCW 64.6 51.3 17.0 20.0 5.6 6.0 2.5 11.5 1.5 4.5 1.0 4.2 1.3 2.9 3.2 0.7 0.8 0.6 1.1 2.70 2.72 590 512 Quartz Quartz Feldspar Feldspar Hematite Mica Regarding the mineralogical composition of cements, ArgPC has more C3S than the CzPC, but the last-one has more C3A and more gypsum that the ArgPC; with respect to their C2S and C4AF content they are similar The mineralogical composition of ceramic wastes was glassy phase, quartz, feldspars (mainly anorthite in ArgCW; albite and orthoclase in CzCW), high content of muscovite in CzCW and hematite in ArgCW The CW was incorporated to blended cement with 8, 16, 24, 32 and 40 % of replacement by weight of cement For all blended cements, the pozzolanic activity, the heat liberation rate and hydrated compounds identification by XRD were determined Pozzolanic activity was determined by Frattini test according the procedure described in EN196-5 at 2, and 28 days The method consists in the determination of the amount of Ca2+ and OH- in the water of contact with the samples stored at 40 °C The ceramic wastes may be considered as an active pozzolan when the [CaO] and [OH-] of their solution are located below the solubility isotherm of calcium hydroxide Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 210 V Rahhal et al / Utilization of Ceramic Wastes as Replacement of Portland Cements The heat released rate was determined for 48 hours in an isothermal calorimeter operating at 20 °C, the amount of blended cement was 20 g and the water-tocementitous ratio was 0.50 XRD analysis was made on ground pastes cured in sealed condition at 2, and 28 days The determinations were performed on Philips PW 3710 diffractometer with Cu KD operating radiation 40 kV and 20 mA using carbon monochromator Results and discussion Figures and show the results of Frattini test on the [CaO] vs [OH] plot for the blended cement ArgPC-ArgCW and CzPC-CzCW at 2, and 28 days, of respectively Copyright © 2014 IOS Press All rights reserved Figure Frattini test of ArgPC with ArgCW Figure Frattini test of CzPC withCzCW At days, both cements with to 40 % of ceramic waste have not pozzolan activity, because all points are above the calcium solubility isotherm at the super saturation zone The [CaO] increases when increase the level of replacement showing the stimulation effect on the hydration of cement At days, the reduction of [OH-] and [CaO] shows that ceramic wastes have pozzolanic reactivity and the blended cement with high replacement level became bellow the solubility isotherm at the calcium sub saturation zone At 28 days, all blended cements appear with good pozzolanic activity and this is more evident when the replacement level of CW increases The results of calorimetric test for ArgPC-ArgCW and CzPC-CzCW blended cements are given in Figures and 4, respectively For both systems, it can be observed that the increase of replacement level from to 40 % produces a low heat liberation rate and low accumulated heat This observation can be attributed to the dilution effect [5] For the ArgPC-ArgCW blended cements, the acceleration slope of the second peak in the calorimetric curve is reduced and it remains with slight changes for the CzPCCzCW blended cements The high C3A content of the CzPC produces the third peak, which is not reveled in pastes with the ArgPC (low C 3A) Form the CzPC-CzCW, it can be observed that the CW-addition stimulates the cement hydration, specially the aluminic phase, because the intensity of the second peak decreases more than the intensity of the third peak when the replacement level of CW increases All blended cements exhibited the maximum of the hydration heat at approximately 14 hours reveling that CW acts without interference in the cement Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 E.-O.E Agbenyeku and F.N Okonta / Mechanical Properties of Green Concrete 429 are presently performing well and no structural deficiencies have at yet been experienced or recorded Nevertheless, it was noted by [4] that fly ash (FA) used as cement replacement for PNS concrete had negative effects on the compressive strength of the concrete product with a strength reduction of up to 29% It was also revealed that the compressive strength of PNS concrete was found to be within the range acceptable for structural LWGC, which was about 50% lower than the ordinary concrete, and that the PNS concrete gained its highest strength within a 56days hydration period The use of PNS therefore, as coarse aggregate in LWGC production with different hydration schedules over a 56days period will have effects on compressive strength, density and workability of the LWGC product Certain established methods such as; ACI method for normal weight concrete and other similar methods as recorded by [5, and 7] could not be applied as mix design for PNS concrete A trial mix design for concrete with PNS aggregate as coarse aggregate yielded a compressive strength of 24 N/mm2 for a hydration period of 28 days [5] Fly ash as mineral admixture and calcium chloride as an accelerator were also used to study the improvement in strength of the concrete Meanwhile, High Strength Concrete according to [8] is set to achieve 40 Mpa (6000psi) compressive strength over 28 days hydration period although, it should be taken into cognizance that it depends on geographical and concreting conditions Hence, the abundance of PNS in West Africa has paved way for PNS to be studied as replacement for coarse aggregate in green concrete where series of laboratory tests are conducted on the fresh and hardened LWGC specimens Copyright © 2014 IOS Press All rights reserved Materials and methods The materials used in this study are portable tap water for mixing and curing the concrete, ASTM Type I Ordinary Portland Cement, coarse aggregate with particle size distribution between to 14mm, PNS were obtained in sufficient quantities from Ikoritungko Oil Milling Factory located around Calabar, Nigeria (see Figure 4) All impurities and injurious contents such as oil remains and dirt were removed from PNS by a thermal process The PNS was left in the oven under high temperatures of about 150-1700C for close to 24 hours Series of laboratory works were conducted to investigate the effects of PNS on workability and compressive strength of the new concrete type, when used as partial replacements for coarse aggregates The tests carried out included; the slump test which was done in accordance to B.S 1882 part II, the compaction factor test was done in conformance to B.S 1881:1970 part II to test the workability of concrete, the Schmidt hammer or Surface Hardness-rebound test based on BS 1881 Part 202 and the compressive strength test which was done according to BS 1881 Part 116 for strength determination of concrete Figure Inner cot of palm Figure PNS collected as waste Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 430 E.-O.E Agbenyeku and F.N Okonta / Mechanical Properties of Green Concrete All the samples were cured at relative humidity (RH) of 95-100% and temperature (T) of 22-25 C in a chamber for different hydration ages of 7, 14, 21 and 28 days [9] A mix proportion for LWGC as earlier stated is different from the mix proportion of high strength concrete or normal strength concrete For the LWGC, which is to be produced from using PNS as aggregate partially replacing the conventional coarse aggregate, requires an average cement/water ratio as indicated by [6] Thus, a cement/water ratio of 0.5 was initiated in this study with mixing ratio of 1:2:4 The cubic samples were cast in metal moulds with dimensions of 100 x 100 x 100 mm3 For every batch of PNS concrete mix, Table shows the weight of cement, the fine sand and the crushed aggregates used Table Quantities of concrete constituents in every batch of PNS concrete mix Samples P0 P10 P20 P30 P40 P50 Total %PNS 10 20 30 40 50 OPC 1.157 1.157 1.157 1.157 1.157 1.157 6.942 Sand 2.314 2.314 2.314 2.314 2.314 2.314 13.884 Gravel 4.63 4.17 3.70 3.24 1.39 2.32 19.45 PNS 0.0 0.43 0.93 1.39 3.24 2.32 8.31 Total 8.101 8.101 8.101 8.101 8.101 8.101 48.61 Discussion of results The workability of concrete batches for the respective percentages of PNS mix using the slump test was presented in Figure The mix samples with constant w/c ratios of 0.5 were found to display medium to high workability It further showed that as the percentage replacement of PNS increased, workability of LWGC reduced except for 10%PNS where it showed a spike in workability The specific surface was also found to increase as the PNS content increased The plausible explanation to these behaviours can be because the control aggregate was denser than the PNS aggregate and the replacement in this study was done by weight This led to more cement paste been required to lubricate the aggregate as such, reduced the entire fluidity of the mix which subsequently reduced the height of the slump SLUMP HEIGHT AGAINST PNS REPLACEMENTS 60 SLUMP HEIGHT (mm) Copyright © 2014 IOS Press All rights reserved 3.1 Slump test 40 20 0 10 20 40 PNS (%) 30 Figure Effects of PNS replacements on slump height of respective mixes 50 Consequently, the decreased slump height in the 20, 30, 40 and 50% mixes as the percentage of PNS increased was attributed to w/c ratio; having w/c ratio of 0.5 used for the respective mixes, the hydrated cement paste became more watery and less viscous This process allows the penetration of cement into the PNS aggregate Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 E.-O.E Agbenyeku and F.N Okonta / Mechanical Properties of Green Concrete 431 Additionally, it reduces the amount of cement paste available for lubrication and hydration which resulted in decreased free flow of cement paste in the mix and thereby, causing a decreased slump A test by [2] was conducted using Palm Kernel Shells (PKS) as replacement for the control aggregate which displayed similar behaviours recorded by PNS aggregate in this study As the percentage of PKS increased, the workability of the concrete was reported to reduce as such, the height of slump reduced 3.2 Compaction factor test COMPACTION FACTORS The compaction factor test was conducted to check the workability of the respective concrete mixes Although the workability of the concrete was first checked by slump test however, the compaction factor test was further conducted to validate the accuracy of the results The compaction factor of the concrete mixes for the respective percentages of PNS as replacement for the coarse aggregate was shown in Figure COMPACTION FACTORS AGAINST PNS REPLACEMENTS 0.95 0.9 0.85 0.8 10 20 30 40 PNS (%) Figure Effects of PNS replacements on compaction factors of respective mixes 50 Copyright © 2014 IOS Press All rights reserved From the results gotten from the compaction factor test, it was observed that the 10%PNS sample had the highest compaction factor of 0.9 It can also be seen that similar to the slump test, after the 10%PNS replacement, the compaction factor decreases The decrease in the compaction factor value after a steep rise from 0-10% PNS replacement may have resulted from the sensitivity of workability test or because the control aggregate was denser than the PNS aggregate and the replacement in this study was done by weight Furthermore, it was seen that all compaction factor values for the entire sample mixes were within the acceptable ranges from medium to high workability 3.3 Density of specimens The densities of the tested samples were determined to find the possibility of using LWGC as a structural element Average densities of three specimens were determined as the actual density of each percentage mix Table shows the densities of the samples with the respective percentage of PNS replacements Figure shows the densities to reduce as the percentage of PNS increases vice versa, with the range of densities for PNS concrete for 28 days to be between 2278–1975 kg/m3, while the 0%PNS concrete (as control) had a density of 2473 kg/m3 The highest density, 2473 kg/m3, was recorded for 0%PNS, while the least density 1975 kg/m3 was recorded for 50%PNS As established in hypothesis of this study, concrete strength was expected to decrease as the %PNS increases This contributes to the properties of LWGC from PNS aggregates having a density lesser than 2000 kg/m3 This became approximately 60% Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 432 E.-O.E Agbenyeku and F.N Okonta / Mechanical Properties of Green Concrete lighter as reported by [4 and 7] in comparison to the conventional crushed stone aggregate, which then results in the production of LWGC The LWGC having a density lesser than 2000 kg/m3 indicated that the 40 and 50%PNS samples are considered LWGC with densities of 2047 and 1975 kg/m3 respectively An expected density for control sample was in the range of 2400 kg/m3 as such, the 0%PNS concrete was considered a normal weight concrete Hydration period 14 21 28 0% PNS 2430 2451 2462 2473 Table Density of respective specimens 10% 20% 30% PNS PNS PNS 2241 2121 2065 2254 2134 2088 2263 2172 2120 2278 2194 2133 40% PNS 1978 1992 2011 2047 50% PNS 1899 1923 1932 1975 DENSITY OF CONCRETE SAMPLES (kg/m3) The 40 and 50%PNS is been considered a lightweight concrete for the fact that the 10,20, and 30%PNS had a higher coarse aggregate to PNS aggregate ratio This shows that coarse aggregate has a larger volume in the mix than PNS aggregate, and since coarse aggregate is heavier than PNS aggregate, the concrete specimen was denser 3000 DENSITY AGAINST HYDRATION PERIOD FOR THE RESPECTIVE PNS REPLACEMENTS 0% 10% 20% 30% 40% 50% 2500 2000 1500 1000 500 14 21 28 HYDRATION PERIOD (days) Figure Density of samples with respect to hydration periods Copyright © 2014 IOS Press All rights reserved The LWGC maybe have been produced due to the amount of w/c ratio used in the study An increase in w/c ratio resulted in a decrease in cement content and increased the water content which reduced the overall weight of the concrete An additional possibility could be the actual weight of coarse and PNS aggregate used Hence, the Table and Figure show that an increase in PNS aggregate led to a decrease in the density of the product Nonetheless, since PNS aggregate is lighter in weight, the replacement of coarse aggregate at different percentages resulted to a lesser amount of coarse aggregate in the mix; the absorption of cement paste was reduced as PNS aggregate not firmly bond with cement thereby, reducing the overall density of concrete and then creating a LWGC 3.4 Schmidt hammer test The Schmidt hammer test was conducted to determine the strength of samples by measuring the surface hardness of concrete Schmidt hammer test results for PNS samples showed that the strength of the samples increased with age as seen in Figure This test is very similar to the compressive strength test The results from the test revealed a substantial extension in concrete strength as the hydration period extended and as the %PNS in each sample reduced, with 0%PNS recording the highest strength Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 E.-O.E Agbenyeku and F.N Okonta / Mechanical Properties of Green Concrete 433 CONCRETE STRENGTH (N/mm2) and 50%PNS had the least concrete strength 47.3 N/mm2 and 22.7 N/mm2 at 28 days In the case of the Rebound hammer test however, the concrete strength depreciated when compared to the compressive strength test results in Figure The difference was accounted for by the concrete surface area which is affected by its rough surface due to the presence of PNS in the sample 60 CONCRETE STRENGTH AGAINST HYDRATION PERIOD FOR THE RESPECTIVE REPLACEMENTS 40 20 0% 10% 20% 30% 40% 50% 14 21 28 HYDRATION PERIOD (days) Figure Concrete strength of samples with respect to hydration periods Inclusive factors maybe in relation to the angle of inclination or the Schmidt hammer It is clear from the results that both Schmidt hammer and compressive strength test have a strong correlation which can be the reason 0%PNS had a higher strength and 50%PNS is made of higher quantity of organic materials that happen to be lighter and less stronger than the conventional coarse aggregate 3.5 Compressive strength test The compressive strength of the crushed specimens in this work is reciprocal to the %PNS used From Table and Figure respectively, the compressive strength development of concrete with age is observed Table Compressive strength of respective specimens Copyright © 2014 IOS Press All rights reserved Hydration period 14 21 28 0% PNS 42.3 49.6 54.4 59.5 10% PNS 37.1 39.6 42.5 48.7 20% PNS 33.6 37.3 39.5 41.6 30% PNS 22.8 33.1 36.7 39.2 40% PNS 18.6 26.3 29.8 32.1 50% PNS 13.7 22.5 24.8 28.7 It shows the effect of the different amount of PNS on the strength of the concrete The rate of strength gain was pronounced as the hydration period increased i.e., as the %PNS increased, the compressive strength of the concrete decreased, vice versa While the strength of the concrete decreased as the %PNS increased The 0%PNS had the highest strength although, as PNS replaced the coarse aggregate the concrete strength gradually decreased The plausible explanation is the fact that PNS are organic materials lighter and less strong than the conventional coarse aggregate It also could be attributed to the highly irregular shapes of PNS, which prevented full compaction with normal coarse aggregate hence, affecting the strength of the concrete Furthermore as recorded by [5], the weak bond between PNS and cement paste as compared to the control samples may have caused the reduction in strength due the smoothness of the sample Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 COMPRESSIVE STRENGTH (N/mm2) 434 E.-O.E Agbenyeku and F.N Okonta / Mechanical Properties of Green Concrete 60 COMPRESSIVE STRENGTH AGAINST HYDRATIION PERIOD FOR RESPECTIVE REPLACEMENTS 40 20 0% 105 20% 30% 40% 50% 14 21 28 HYDRATION PERIOD (days) Figure Compressive strength of samples with respect to hydration periods Nevertheless, with respect to the general strength of samples, it was observed that all mixes produced high strength concrete at age 28days As defined by [8] a high strength concrete generally is a high performing concrete with specific compressive strength of up to 40 MPa (6000psi) and beyond Considering the 28days in reference to hydration periods; 0, 10 and 20%PNS satisfied the requirements of high strength concrete Even though at 7days early hydration stages, some concrete samples obtained very high strength values The compressive strength developed for 50%PNS in 28days, was above the range of 20.10–24.20 N/mm2 requirement for structural LWGC elements Copyright © 2014 IOS Press All rights reserved Conclusions This study illustrated some mechanical properties of green concrete produced from PNS as coarse aggregate The abundance of PNS in West Africa paved way for PNS to be studied as replacement for coarse aggregate in green concrete From a perspective of strength and workability, and in conformance to waste recycled materials, PNS aggregate was founded to be a good substitute of coarse aggregate in concrete production From results and analysis however, the following conclusions were reached; x The PNS samples had relative medium to high workability ranging from 2447mm for slump height, and 0.85-0.90 for compaction factor x Not all PNS concrete samples fully satisfied the structural light weight concrete requirement, with only 28 days 50%PNS concrete sample been within the density limit of 2000 kg/m3 for structural lightweight concrete although, 10,20,30 and 40%PNS samples could be considered as partial lightweight concrete x The general strength of 10,20 and 30%PNS concrete samples produced high strength concrete with compressive strength reaching up to 48.7 N/mm2 for 28 days, which satisfied the requirement for high strength concrete The 30%PNS is therefore, the ideal percentage of PNS which is in the boundary limit for the production of high strength concrete, however it is considered as partial lightweight concrete x The samples with 10%PNS and 50%PNS had the highest and least compressive strength respectively, which signified that the compressive strength of PNS concrete samples is dependent on the amount of PNS aggregate in the sample; although, the strength of the samples are dependent on the amount of PNS and Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 E.-O.E Agbenyeku and F.N Okonta / Mechanical Properties of Green Concrete x 435 the hydration period, the least desirable structural requirement for light weight concrete was met Finally, this paper demonstrates how the use of PNS as yet another option in transforming abundantly available cheap agricultural waste into useful resource for developing countries Hence, the green concrete product can at the moment be utilized in the construction of light weight simple foundations and masonry walls while further investigations are recommended to be carried out on the effect of admixtures on PNS concrete over an extended hydration period of up to 120days References [1] [2] [3] [4] [5] [6] [7] [8] Copyright © 2014 IOS Press All rights reserved [9] Alengaram U.J., Hilmi Mahmud and Mohd Zamin Jumaat, Comparison of Mechanical and Bond Properties of Oil Palm Kernel Shell Concrete with Normal Weight Concrete, International Journal of Physical Science, Vol 5(8), pp.1231-1239, 2010 Teo D.C.L., Mannan, and V.J Kurian , Flexural bahaviour of Reinforced Lightweight Concrete Beams made with Oil Palm Shell, Journal of Advanced Concrete Technology, Vol 4, No 3, pp 459-468, 2006 Alexander M.G and Sydney Mindness, Aggregates in Concrete, Taylor and Francis Publication, Abingdon, 2005 Teo D.C.L., Man.nan, and V.J Kurian , Structural Concrete Using Oil Palm Shell (OPS) as Lightweigh Aggragate, Turkish J Eng Env Sci, Vol 30, pp 1-7, 2006 Mannan M.A, Ganapathy C 2001, Mix Design for Oil Palm Shell Concrete, Cement and Concrete Research Vol-31, Issue (2001), pp 1323-1325 Mannan M.A., Ganapathy C 2004, Concrete from an agricultural waste-Oil Palm shell, Building and Environment Vol-39, Issue (2004), pp 441-448 Payam Shafigh, Mohd Zamin Jumaat and Hilmi Mahmud, Mix Design and Mechanical Properties of Oil Palm Shell Light Weight Aggregate Cocrete: A Review Paper, International Journal of the Physical Science, Vol 5, No 14, pp 2127-2134, 2010 Portland Cement Association, Concrete Technology Today, High Strength Concrete, Vol 15, No 1, March 1994 TMH1 1986 Standard Methods of Testing Road Construction Material, Technical Methods for Highways Vol 11 Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 436 Construction Materials and Structures S.O Ekolu et al (Eds.) IOS Press, 2014 © 2014 The authors and IOS Press All rights reserved doi:10.3233/978-1-61499-466-4-436 New proposed direct tensile strength test for concrete M Iqbal KHAN1 and Shehab MOURAD Department of Civil Engineering, College of Engineering King Saud University, Saudi Arabia Abstract The evaluation of the tensile strength and determination of the tensile stress-strain curve using indirect tests becomes approximate hence there is a necessity for exploring direct tensile strength measurement This investigation is part of ongoing research on the development of direct tensile strength measurement In this paper direct tensile strength test has been proposed and the results obtained have been compared with compressive strength and flexural strength It has been found that results obtained are well comparable and relationships are similar to that proposed in earlier findings Keywords Direct tensile strength, flexural strength, compressive strength Copyright © 2014 IOS Press All rights reserved Introduction Tensile strength of concrete is of prime importance in case of water retaining structures, runway slabs, pre-stressed concrete members, bond and shear failure of reinforced concrete members and cracking of mass concrete works Practicing Engineers working with reinforced concrete ignore the low value of the tensile strength of concrete and use steel to pick up tensile loads With massive concrete structures, such as dams, it is impractical to use steel reinforcement Therefore, a reliable estimate of the tensile strength of concrete is necessary, especially for judging the safety of dam under seismic loadings [1] The tensile strength of concrete is much lower than its compressive strength, largely because of the ease with which cracks can propagate under tensile loads Although tensile strengths are usually not considered directly in design (being assumed to equal zero), they are quite important, since cracking in concrete tends to be a tensile failure However, the relationship between tensile and compressive strengths is not a simple one It depends on the age, strength of the concrete, the type of curing, the type of aggregate, the amount of air entrainment, and the degree of compaction Present research work has been mostly done on the evaluation of tensile strength of concrete by indirect methods and comparatively fewer efforts have been made for its determination by direct methods The behavior of concrete under tension has not been extensively investigated because of its limited tensile strength and extensibility [2] Corresponding author: miqbal@ksu.edu.sa Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 M.I Khan and S Mourad / New Proposed Direct Tensile Strength Test for Concrete 437 Although concrete is never made to carry tension, yet tensile cracking of concrete limits the usefulness as well as life of several structures For such cases formulation of the behavior of concrete under tension is needed for the development of structural theory There is the need of standard methods and size of specimen for the determination of tensile strength of concrete [3] None of the existing methods for determination of tensile strength of concrete compare favorably as regards reproducibility or reliability with compression test [4] The determination of tensile strength and the stress-strain curve in tension for brittle materials such as cement mortar and concrete is not a straight forward affair Arrangement of suitable loading and gripping devices to create uniform tensile stress in a test specimen encounters major problems which resulted in accepting indirect tensile measurements to be a practical alternative measurement The indirect tests not create a strictly uniform tension on the failure surface and often the stresses on the failure surface are not uniaxial Therefore, determination of the tensile strength becomes approximate and in addition, determination of the tensile stress-strain curve from the above mentioned indirect tests is difficult Hence there is a necessity for exploring direct tensile strength measurement Experimental program 1.1 Materials and mix design Cement Type I complying with the requirements of the ASTM C150 was used in this investigation Fine and coarse aggregates available in the laboratory were used for this investigation Grading limits of fine and coarse aggregates were in accordance with ASTM C 33 Both the fine and coarse aggregates were air-dried before use, and allowance was made for absorption when calculating batch weights Water to cement (w/c) ratios at 0.30, 0.40 and 0.50 were used The dosage of superplasticizer was maintained to attain an initial slump between 120±20 mm The mix design used in this study is as per ACI 211.1-91 The summary of the mix proportions are given in Table The measurements were taken at and 28 days, in accordance to ASTM standards Triplicate samples were tested for each age and the mean value is reported as the result Copyright © 2014 IOS Press All rights reserved Table Design of mixes with different water-cement ratios Materials Mix Mix Mix Cement (kg/m3) 520 446 350 Fine aggregates (kg/m3) 600 600 780 Coarse aggregates (kg/m3) 1040 1040 1050 Superplastisizer dosage Maintained initial slump at120±20 mm w/c 0.30 0.40 0.50 Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 438 M.I Khan and S Mourad / New Proposed Direct Tensile Strength Test for Concrete 1.2 Testing procedure There is no standard method for measurement of direct tensile strength In this investigation directed tensile test measurement is proposed which is based on pullout direct tension The specimen used for this test method was 76 x 76 x 305 mm as shown in the Schematic Diagram, Figure The specimens are notched at mid-height, providing for a nominal cross section at the failure zone of 51 x 76 mm [5], by using two pieces of wood to reduce the cross section of the material at the middle as shown in Figure To apply the tensile force to the concrete two pieces of reinforcement steel (8 mm bar) were placed as shown in Figure The total length of each piece was 200 mm and 100 mm was placed inside the concrete One end of the rod was fixed with plus shaped anchor (6 mm bar) to get the grip in the concrete The concrete was casted in these specially prepared molds as show in Figure The final shape of the specimen is presented in Figure Testing arrangement and typical failure modes are shown in Figures and 7, respectively This test method involves the measurement of the force required to pull out a previously cast-in steel bar Because of the shape of the specimen, the steel bar assembly is pulled out with a crack on its body The pull out strength is calculated as the ratio of the force to the area of the cross section, the strength being close to that of the shearing strength of concrete This test comprises of a concrete prism with embedded steel The steel bars are connected to the clutches of the pullout machines and at the failure the maximum load upon fracture and the location of the facture is noted down Then the tension resistance is calculated as: ft P A where: ft = Direct tensile strength; A = Area of web at failure point (1) P = Load of the web at failure point Copyright © 2014 IOS Press All rights reserved In order to validate the results obtained for the tensile strength of concrete, compressive strength, and flexural strength measurements were also conducted in accordance to ASTM standards Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 M.I Khan and S Mourad / New Proposed Direct Tensile Strength Test for Concrete 439 Figure Schematic diagram of direct tension arrangement Copyright © 2014 IOS Press All rights reserved Figure Shape of specimen Figure Shape of pullout rod Figure Mould arrangement Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 440 M.I Khan and S Mourad / New Proposed Direct Tensile Strength Test for Concrete Figure Shape of direct tension specimen Figure Direct tension test in progress Copyright © 2014 IOS Press All rights reserved Figure Typical direct tensile failure Results and discussion 2.1 Compressive strength The compressive strength development of concrete is shown in Figure It is evident from this figure that compressive strength decreases with increase in w/c ratio, as expected Mix-1 having w/c ratio 0.30 attained compressive strength 72.4 MPa and 82.9 MPa at and 28 days, respectively At days, Mix-2 and Mix-3, having w/c ratios of 0.40 and 0.50 are 41% and 46% lesser than the Mix-1, respectively At the age of 28 days Mix is 41% and Mix-2 is 32% lesser than the Mix-1 Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by S.O Ekolu, et al., IOS Press, 2014 ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/hustvn-ebooks/detail.action?docID=1920292 Created from hustvn-ebooks on 2017-09-05 00:46:01 M.I Khan and S Mourad / New Proposed Direct Tensile Strength Test for Concrete 441 2.2 Flexural strength Figure demonstrates the flexural strength development of concrete The trend of the results of flexural strength is similar to that of compressive strength As expected, Mix1 attained maximum flexural strength at both ages investigated Mix-1 had a flexural strength gain of 12% from to 28 days whilst Mix-2 and Mix-3 gained 33% and 17%, respectively 2.3 Direct tensile strength The direct tensile strength development of concrete is demonstrated in Figure 10 It clearly shows the similar pattern of strength development as in case of compressive and flexural strengths (Figures and 9) As w/c ratio increases the direct tension decreased uniformly, as expected Direct tensile strength development of Mix-1 having w/c ratio 0.30 showed 4.81 MPa and 5.37 MPa at and 28 days, respectively As being an indirect tensile measurement, flexural strength showed 8.32 MPa and 9.33 MPa which is at least 40% higher than that of direct tensile measurements For Mix-2 (w/c 0.40) and Mix-3 (w/c 0.50) the flexural strength were also higher at both ages investigated, however, the rate of increase in the flexural strength is between 30 and 20% It is evident for the results that the flexural strength measurement shows higher results than that of direct tensile measurements This trend of increase can be seen from Figure 11 which shows the relationship between direct tensile strength and flexural strength The empirical relationship for the direct and indirect tension is as follow: ft 1.57 f f 0.55 (2) where: ft - is direct tensile strength (MPa) ff - is flexural strength (MPa) Copyright © 2014 IOS Press All rights reserved Similarly, relationship between direct tensile strength and compressive strength has been shown in Figure 12 for the sake of comparison and its empirical relationship is as follow: ft 0.50 f cu 0.54 (3) where: fcu - is compressive strength (MPa) Equation is similar to that proposed by ACI which is as follows; Vt 0.62V c ... Portland cement pastes Construction and Building Materials 51 (2014), 484-491 Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and. .. Geotechnical Engineering and Geomorphology”, England, Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited by... Material, Cement and Concrete Research 26 (1993), 856-890 Construction Materials and Structures : Proceedings of the First International Conference on Construction Materials and Structures, edited