Microsoft Word 277 BUi Ngoc Kien doc Tuyển tập Hội nghị Khoa học thường niên năm 2019 ISBN 978 604 82 2981 8 81 EXPERIMENTAL ANALYSIS OF RECYCLED AGGREGATE CONCRETE BEHAVIOR UNDER CONFINEMENT PRESSURE[.]
Tuyển tập Hội nghị Khoa học thường niên năm 2019 ISBN: 978-604-82-2981-8 EXPERIMENTAL ANALYSIS OF RECYCLED AGGREGATE CONCRETE BEHAVIOR UNDER CONFINEMENT PRESSURE Ngoc Kien Bui1, Truong Viet Hung2 Department of Civil Engineering, Thuyloi University, email: kienbn@tlu.edu.vn Department of Civil Engineering, Thuyloi University, email: truongviethung@tlu.edu.vn INTRODUCTION Recent years, with the outbreak development of construction industry, the demands of concrete have been increasing relentlessly about 15 billion tons annually, which accompanied by a huge requirement in consuming aggregate product approximately 10-11 billion tons each year [1] Besides, increase of large quantities of the construction and demolition waste (CDW) due to the end of service life of infrastructures, war, natural disasters and human activities cause extreme challenges for environment protections and construction industry [2] It is estimated that the amount of construction and demolition waste occupies about 40% of the total waste, which was indicated in studies of Takahashi et al.(2011), becoming burdens of many nations For that reason, recycling CDW as a new aggregate source for concrete has received much more attention due to its feasibility, environmental and economic benefits [4] Using RCA for concrete structures in many countries is still controversial and not easy to come to life because of the lower qualities of RAC and more complicated microstructure such as contained large flat Ca(OH)2 crystal (CH crystal, about 20-25% of the volume of solids in the hydrated paste) which accumulated in the voids and the surface of RAC [5]; a huge amount of pores and cracks [6]; especially it holds two interfacial transition zone (ITZ), one is new ITZ between RCA and new cement paste and another one is old ITZ between old natural aggregate and old adhered mortar [7], compared to natural aggregate concrete (NAC), which causes negative effects on performance of RAC [8] Which is why, numerous studies have been conducted to evaluate and improve the mechanical and durability properties of RAC [9] To enhance the properties of RAC, several techniques have been developed in the literatures [10] Recently, it is believed that using pretreating method for RCA, surface modification treatment of RCA with pozzolanic admixtures or enhancing the microstructure of RCA is a good solution for improving the qualities of RAC [5] is one of great solution for saving consumption energy and environmental friendly It may be reasonable to recognize that pozzolanic admixtures can enhance microstructure by two reasons: one is pozzolanic admixtures plays as a micro filler, filling into pores and cracks of RCA, second is pozzolanic materials will consume CH crystals in RAC to form CSH gel (Calcium silicate hydrate) to fill up in voids of RCA Thus, the existing methods have improved mechanical properties of RAC in certain somewhat extent and microstructure of ITZ still existed much amount of CH crystal Therefore, in this paper we proposed a solution (including pozzolanic powder and sodium silicate) for pre-treating RCA in order to improve the properties of microstructure in RCA with the purpose of creating twofold efficiency in reducing maximally the amount of CH in RAC Furthermore, in order to apply RAC for real structure, it is necessary to understand the behavior and performance of concrete under different stress states such as uniaxial stress and triaxial stress because in structure, concrete is often subjected to combinations of compressive, tension and shear stress However, there is lack of experimental reports related to triaxial compressive characteristics of 81 Tuyển tập Hội nghị Khoa học thường niên năm 2019 ISBN: 978-604-82-2981-8 RAC under high confinement pressure particular of RAC contained pozzolanic material Therefore, the aim of this study is to propose the solution for improving the mechanical properties of RAC as well as to investigate the behavior of RAC under unconfined and confined compression pressure METHODOLOGY FOR PRETREATING RCA Treatment solution was proposed to improve the quality of RCA and the detail of treatment solutions (pozzolanic solutions) components are composed of sodium silicate and one of pozzolanic powder, as in Table Different pozzolanic solutions were prepared with 20% concentrations Pozzolanic solution type S which is combination of pozzolanic powder and sodium silicate (Na2SiO3) Table Components of pozzolanic solution type S Concentr ation of solution 20% Components of treatment solution for 1000g Na2SiO3 (g) Pozzolanic powder (g) Water (g) 75 125 800 EXPERIMENTAL PROGRAM 3.1 Materials Mixture design proportion of RAC for a target concrete strength was selected water cement ratio and slump for rigid pavement application and the water/cement ratio was kept constant at 0.45 The amount of water used for each batch is different because of the difference of water absorption of each aggregate blend The mix proportions of concretes are represented in Table 3.2 Equipment for testing The compressive strength of concrete is measured by Shimadzu machine with 1000kN axial load capacity at a rate of axial loading constant at 0.25MPa/s The high pressure of chamber was provided by pump for triaxial compression test RESULT AND DISCUSSION 4.1 Triaxial compression test The testing machine was setup as shown in Fig 1, the axial load from the testing machine is transmitted to specimen inside oil chamber by a piston The pressure in chamber was provided by an oil pump The specimen, before put into the chamber, was wrapped by polyolefin tubing which is shrinkable in heat condition (Sumitube-Sumitomo electric branch) Two levels of confining pressure (15MPa and 25MPa) were used in order to study the mechanical behavior and brittleductile transition of RAC The RAC specimens was at 108 days of age to minimize the effect of aging on the response It can be seen that at SFA and SMT, the specimen was broken suddenly into two or three pieces while the failure occurs with the propagation of several distributed vertical and inclined cracked at SSF In Fig 2, the maximum axial stress or confined compressive strength and unconfined compressive strength for each confining pressure was pointed out that the peak stress of RAC increases with increasing the confinement Table 2: Mix proportion of concrete kg/m3 Sample Water Cement 228.2 428.9 823.2 670.7 SSF 236.8 428.9 804.1 670.7 SMT 232.6 428.9 808.4 670.7 machine Load cell Chamber Pump for confining pressure Coarse Fine aggregate aggregate SFA Testing Fig Testing setup for triaxial test 82 Tuyển tập Hội nghị Khoa học thường niên năm 2019 ISBN: 978-604-82-2981-8 Moreover, although at uniaxial compression test the obtained result show the highest value at SSF, the peak stress of SFA is highest value at all confining pressures compared to others The Fig shows initial tangent modulus of RAC at high confinement pressure levels, it can be seen that the value of initial tagent modulus of RAC treated with SFA at confining pressure is higher than others even at unconfining level the modulus of this sample is lower than others From the result of triaxial test, Mohr stress circles were constructed then it should be drawn the tangent to the Mohr circles to determine the initail shear stregnth of RAC as illustrated in Fig It can be indicated that the initial shear strength of SSF is higher than others, which proved that SSF at high confining pressure level is more vurnarable than SSF, SMT Fig Maximum stress of RAC under confined and unconfined compression Fig Modulus of elasticity of RAC under unconfined compression and initial tangent modulus of RAC under confining pressure Fig Initial shear strength of RAC CONCLUSIONS As an attempt to improve the quality of RAC by using treatment solutions of RCA with different of pozzolanic materials was investigated in this study From the experimental results, the important conclusions are summarized as following: Treatment solutions for RCA can enhance compressive strength of RAC considerably, treatment solution type SSF was more effective than others at uniaxial compression stress, but, at high confining pressure its strength was lower than others Treatment solution for treating RCA significantly affected the mechanical properties of RAC at uniaxial loading and triaxial loading conditions Pozzolanic materials such as fly ash, silica fume and metakaoline combined with sodium silicate was recommended to treating RCA The results of triaxial compression test were performed at high confinement on RAC specimens, which revealed the significant differences in maximum stress This was attributed to the influence of confinement pressure and treatment solutions In brief, the results obtained from this study demonstrated the feasibility of this method for applying in real condition in improving strength of RAC However, in order to apply this technique in the field, it is necessary to conduct researches on durability of concrete In the further study, we will resolve relevant issue related to durability and performance of concrete after treated with treatment solutions REFERENCE [1] S.B Huda, M.S Alam, Mechanical behavior of three generations of 100% repeated recycled coarse aggregate concrete, Constr Build Mater 65 (2014) 574–582 [2] H Takahashi, M Ando, DEM simulation of crushing for concrete blocks by mobile crusher, in: AIP Conf Proc., AIP, 2009 [3] Hiroshi TAKAHASHI, Yuki SANDO, Tomoaki SATOMI, Numerical Simulation on Crushing of Concrete Blocks by Mobile Crusher, in: Proceeding Int Symp Earth Sci Technol 2011, Fukuoka, Japan, 2011 83 ... because of the difference of water absorption of each aggregate blend The mix proportions of concretes are represented in Table 3.2 Equipment for testing The compressive strength of concrete. .. Maximum stress of RAC under confined and unconfined compression Fig Modulus of elasticity of RAC under unconfined compression and initial tangent modulus of RAC under confining pressure Fig Initial... Mechanical behavior of three generations of 100% repeated recycled coarse aggregate concrete, Constr Build Mater 65 (2014) 574–582 [2] H Takahashi, M Ando, DEM simulation of crushing for concrete