INTRODUCTION
Background of Pervious Concrete Pavement
Today, along with the development of modern construction technologies, advanced and environmentally friendly materials are also focused on sustainable development
Concrete is a common construction material in the construction industry in general and technical infrastructure in particular
In particular, Portland Cement Pervious Concrete (PCPC) or Pervious Concrete Pavement
(PCP) is a material that has been researched and applied in recently as an environmentally friendly material
According to the National Mixing Concrete Association (NRMCA), porous concrete is a high porosity concrete used for flat surface concrete applications that allows water from rain and other sources to flow through This will reduce the flow from one location and reload the groundwater level These are also called non-fines concrete and are made of Portland cement, coarse aggregates, water, with little or no sand and additives
The draining water PCP has many merits, such as good safety driving in rainy days, reducing noise, high anti-slippery performance of the pavement and no accumulated water, no splash and spray in rainy days, increasing the driving safety in rainy days greatly The draining water bituminous pavement obtains widespread applications in Western Europe,
US and Japan and so on
Porous concrete is used for pavement materials, it can penetrate rainwater at the source, contributing to improved driving safety, noise while reducing traffic, road heat effects in the capital Marketing is also overcome and contributes to sustainable development
Evaluating the environmental impact of porous concrete with non-porous or conventional concrete also gives different results Porous pavement makes air, water and temperature penetrate into different parts of the environment, from which they undergo different storage, handling and flow processes Therefore, porous concrete is an environmentally friendly material
Research on using fly ash and Blast Furnace Slag also contributes to reducing environmental pollution because Blast Furnace Slag pollutes water and air when left in nature.
Scope and Objective
The study on strength and permeability of PC containing fly ash, slag and silica fume is to achieve the following goals:
- To investigate the effect of fly ash and Blast furnace slag, silica fume on strength and permeability of PCPC
- To achieve PCPC mixture design that has necessary compressive strength and permeability suitable for practical road applications
Pervious concrete pavement has important indicators as strength, permeability, abrasion, surface texture and some other indicators Within the scope of this thesis, the author focuses on two main indicators: strength and permeability of Pervious Concrete Pavement (PCP)
The super plasticizer used in this study is a common polycarboxylate-based SP8P admixture in Japan, which increases the workability, slump for concrete and extends the setting time of cement and concrete
Experimental process of making PCP samples at Komaba Lab, the study carried out the design, tested the compressive strength of concrete according to ACI 522 standard and determined the permeability of PCP according to Park and Tia’s Equation (2004)
By using materials to replace a part of cement such as Blast Furnace Slag (BFS), Fly Ash (FA) with additives such as Super plasticizer (SP) and Silica Fume (SF) to find the optimal mixture PCPC has enough strength and permeability to be applied in practice
Chapter 1: Introduction Chapter 2: Literature review Chapter 3: Methodology and Experiment Chapter 4: Result and discussion
LITTERATURE REVIEW
Introduction of the development of pervious concrete
Leading institutes and associations in the field of concrete pavement in the world:
United States Department of Transportation – Federal Highway Administration (FHWA)
American Concrete Pavement Association (ACPA)
American Association of State Highway and Transportation Officials (AASHTO)
Center for Transportation Research and Education, Iowa State University The issues around PCPC have been investigated as the following table:
Table 2.1 Summary of the research results on PCPC
1 Construction Materials Tennis (2004); Tamai (2003); Kajio (1998)
Porosity and permeability Ferguson(2005); Tennis (2004); Yang (2003)
4 Pervious Pavement Design Kosmatra (2002); Young (2005); Ramadhansyah
PCP using waste material Durability of Porous Concrete
An Experimental study on the water-purification properties of porous concrete
According to research, author Nguyen Van Chanh pointed out that: Pervious Concrete is a type of concrete with continuous pore structure, magnetic porosity (15-35%) having the same composition as normal concrete, however coarse aggregates are used with the same grain size and contain very little or no sand (Nguyen Van Chanh et al., 2005)
When using synthetic stone gravel with smaller size, it increases compressive strength, while increasing porosity in concrete structure and thus increasing the drainage capacity of porous concrete
However, the drainage capacity of porous concrete is not merely secondary to porosity, but is still dependent to many other factors such as continuous counting, winding, pore surface
Water (W) and cement (C): The W/C ratio is determined to be from 0.25 to 0.45 Unlike conventional concrete, the amount of cement in porous concrete is lower than the amount of pore between aggregate particles
When the strength of cement mortar increases, it will lead to an increase in the overall strength of porous concrete Therefore, it is necessary to control the amount of water closely
Using the right amount of water will make the concrete mixture get the desired properties, no mortar phenomenon will flow to the bottom of the bottom layer to fill the pores, causing the drainage of porous concrete
Pervious concrete mix designs in the US include cement, coarse aggregates with a size between 2.54 cm and No 4 sieves and are classified according to the ratio of water/cement
28-day compressive strength of porous concrete ranged from 7 MPa – 24 MPa, with the rate of voids from 14% to 31% and the range of velocity permeability (2-6 cm/min)
Compared to conventional concrete, compressive strength ranges from 3,500 to 4,000psi (28
MPa – 32 MPa), lower than 3,000 psi
Table 2.2 Typical mix design and properties of existing PCPC in the US (reported by Nation
Ready Mix Concrete Association – NRMCA, 2004)
Cement content Coarse aggregate content
Fine aggregate content Water-cement ratio Aggregate to cement ratio Slump lbs/yd 3
Permeability (flow rate) Density (unit weight) Shrinkage
1 to 3.8 MPa 14% to 31% by volume
2 to 36 cm/min (120 to 320 L/m 2 /min)
The Strength of concrete pavement is lower than that of conventional concrete
Therefore, the application of PCPC is limited to low-intensity structures such as parking lots, shoulder lanes, light traffic areas, or roads but not highways
For a wider application, a long-term plan for the study of porous concrete pavements is needed to determine the optimal porous concrete mixing ratio to enhance the strength with suitable permeability to be used highway or highway surface
Nader Ghafoori and Shivaji Dutta reported that both sealed- and wet-curing conditions have shown similar effects on strength development Moreover, the gain in strength, under both curing types, is unaffected by the increase in compaction energy It is found the strength of no-fine concrete increase with rise in compaction energy
The movement of water will be more convenient when the interconnected voids are present in the structure of the permeable concrete When the porosity is higher, the texture is lower in strength and when the porosity is lower, the strength of the porous concrete will be higher (Ferguson, 2005).
Overview of pervious concrete uses Fly ash and BFS additives
Pervious Concrete: ''The new era for rural road sidewalks'' has said:
The objective of the study is to evaluate the cost effectiveness of porous concrete compared to conventional concrete In that study, conventional concrete was used according to the design of the IS Class M20, including 59.25 kg of cement (300 rs/50 kg), 88.88 kg of fine aggregate (600 rs/1 ton) and a total of 177.8 kg (1000 rs/1 ton) (Darshna et al., 2013)
Pervious concrete is used in accordance with the NRMCA guidelines, which are composed of 46.5 kg of cement (300rs / 50kg) and concrete of course (1000rs /1 ton) The conclusion indicates that Porous concrete reduces the flow of rainwater to increase the amount of groundwater to eliminate costly storms for water management practices And that is significant savings in the amount of about 29 rs/m3 or 18 rs/ft2
A study named: “Effect of Aggregate Grading and Cement By-Product on Performance of
Pervious Concrete” also indicates that:
Replacing part of cement with industrial by-products such as fly ash, GGBS has been successfully used as an additional cement material as the target of this study
The author used type 53 cement (specific weight 3.15), coarse aggregate (transmitted through 20 mm and left sieve on 10 mm sieve) together with using GGBS (specific gravity
2.88), fly ash and water (Husain et al., 2015)
Through the research article named: "Evaluation of performance of absorbent concrete using waste materials”, the use of furnace slag, rice husk ash and silica fume and solid waste
(glass powder, ceramic waste, bottom ash) and its effect on strong compressive strength and permeability are as per below:
Usage: Fly ash (2-50%), RHA (10-30%), GGBS (35-70), Silica fume (8-12%), Rubber waste, Glass powder (20-40%) is used to replace part of cement
Research shows that the compressive strength and permeability when using materials have different effects as below:
Fly ash gives long-term compressive strength when increasing but then decreases compressive strength
Rice husk ash reduces more than 10-12% of compressive strength, permeability and durability
GGBFS gives higher strength but lower permeability Silica fume increases compressive strength but does not affect permeability Glass powder strengthens durability and workability and Ceramic powder improves durability (Sukamal et al., 2015)
Author A.Elsayed in the research paper: "Influence of Silica Fume, Fly Ash, Super Pozz and high slag on water permeability and strength of concrete" said that:
Can improve the properties of concrete, such as increasing resistance and reducing permeability by using mineral additives such as fly ash, BFS and silica fume (Elsayed,
In previous studies, increasing the strength of porous concrete will lead to reduce permeability and vice versa In the data sheet you can see, the PCPC strength is about 7-31
MPa That is the limit to expand the application of porous concrete in practice Limitations on strength & durability prevent widespread application of Porous Concrete.
METHODOLOGY AND EXPERIMENT
Methodology
Topics using experimental methods to research The steps for conducting the study include:
The calculation of grading using cement, coarse aggregates, fine aggregates with FA, BFS replaces part of cement, SP and SF as additives based on ACI 522 standard and inherits pervious research results After that, casting samples and testing the strength and permeability of PCPC are conducted.
Experimental procedure
Experiment method: There are four types of tests to characterize properties of pervious concrete mix in this research, including unconfined compressive strength, flexural strength, void ratio and permeability The characterization of tests methods and formulas used for the experiment are indicated as following:
3.2.1 Compressive and flexural strength test
Slump of the fresh concrete is measured following ASTM C143 by a standard cone test
Compressive strength is determined according to ASTM C39, and flexural strength is conducted in accordance with ASTM C78 (using simple beam with third-point loading)
The cylinder specimens with 10cm in diameter and 20cm in length are used for testing compressive strength The prismatic samples 10x10x40cm are for testing flexural strength
Testing machine to test the compressive strength of samples with a capacity of 100 tons is used, cylindrical test samples are aged at 7, 28, 56, 91 days since casting Loading speed is 14 N /mm 2 /minute
The void ratio of pervious concrete is determined by measuring the weight difference between dry samples and water saturated samples
When using the equation of Park and Tia (2004), cylindrical samples with a diameter of 10cm and a length of 20 cm were constructed to check the void ratio:
Vol: volume of sample, cm 3
w: density of water, kg/cm 3 Permeability test
The samples are wrapped in rubber and surrounded by adjustable tube clamps
Cylindrical sample for experiments has a diameter of 10cm and a height of 20 cm The average permeability coefficient (k) is determined as follows according to Das equation
(2) where, k: coefficient of permeability, cm/sec a: area of standpipe, cm 2 L: height of sample, cm A: area of sample, cm 2 t: time for water to drop from h 0 to h t , sec h 0 : height of water in burette at initial time (t = 0), cm h t : height of water in burette at final time (t = t), cm
Ordinary Portland cement (C), Fly Ash (FA) ash, blast furnace slag (BFS) and silica fume (SF) are used in this study
Crushed gravel with the largest size D max 15mm used as a raw aggregate, washed with water before use (G)
Super-plasticizer (SP, a sulfoanated naphthalene formaldehyde condensate of Japanese origin, a dark brown aqueous solution with 42% solids and a density of 1.2) is employed to aid the dispersion of Nano-particles and silica in binder and achieve good workability of concrete
20% sand to coarse aggregate by mass is used, which is expected to enhance strength of pervious concrete
Ordinary Portland cement (OPC) follows JIS R5210 standard, used in this study The physical properties and chemical properties as well as the limit value are specified by JIS
Ground Granulated Blast Furnace Slag (GGBFS) or Blast Furnace Slag (BFS)
Blast furnace slag (GGBS) or blast furnace slag (BFS), is used instead of OPC in this study Blast furnace slag conforms to JIS A6206 and the criteria listed in Table 3.1
Table 3.1 Physical and chemical properties of OPC and GGBS
LOI SiO2 Al2O3 Fe2O3 CaO MgO SO3 Na2O K2O TiO2 P2O5 MnO
- 0.005 Note: “-“: not be specified, “ND”: not be determined
In the process of burning coal in power plants with by-products produced, it is fly ash
Helmuth (Mindes and Young) has shown a summary of the properties and chemical composition of different fly ash
Based on the chemical composition, it is classified as fly ash type F or type C In type F there is a lower amount of High, hence less cement properties and vice versa, C has higher
CaO content, so it has more cement properties and less toxic than F-type fly ash (Elsayed,
The fly ash particles are spherical, and the main chemical components include SiO2, Al2O3 and Fe2O3 The process of using fly ash for concrete mixtures can bring benefits such as improved workability, lower hydration
Besides, when mixing fly ash replaces a part of cement, it also helps concrete with lower cost and improves resistance to sulfate attack
The strength of concrete will also increase with lower porosity in the long term, while improving waterproofing ability
Concrete containing BFS, FA, and SF is manufactured according to the following process:
First water and super-plasticizer are poured into the stirrer and then they are added to stir at high speed for 3 minutes
Then, Cement, fly ash or slag, coarse aggregate and sand are rotated for 30 seconds by mixing dry in the mixer and then the water, SP, SF mixture is poured slowly and mixed for
1 minute, Hold for 1 minute before final mixing for 1 minute
When porous concrete mixing consists of silica fume, cement powder, fly ash or slag, and silica fume, the mixture is mixed under dry conditions in the planetary mixer before 3 minutes
Then the raw aggregate and sand are added to the rotary drum mixer before adding the above mixture and dry mixing for 30 seconds After that, the liquid mixture of additives are poured slowly and mixed for 1 minute, stopping for 1 minute before mixing the last 1 minute
The final fresh concrete is poured into cylindrical molds and prisms prepared for each type of test All cylinders are compacted with 25-fold pokes with skewers 10 mm in diameter and in three layers The outer surface of the mold is lightly tapped 15 times with a mallet after each layer to avoid the concrete sample being pitted around
For a prismatic beam pattern (10x10x40cm), concrete is added to the mold, which is flexed 30 times using a round head with a diameter of 16mm (once for each 14 cm 2 of the upper surface area of the mold), Then, apply external vibration to the four corners of the mold using the hard shaft vibrator for about 3 seconds for each corner
All samples are finished with a steel flight machine after casting Then, to prevent evaporation, plastic sheets used to cover the samples were used
After 24 hours, the samples will then be removed from the molds and soaked in water at a laboratory temperature of about 20-23 degrees C for maintenance in 7, 28, 56 and 91 days until the time of testing Specimens are maintained in the same condition
For a prismatic beam pattern (two samples are placed into a mold made of steel formwork), two layers of concrete are added to the mold with 30 clamps for each layer of each sample and outside the mold, 10 seconds of use Use the vibrator for each of the eight corners after each class
To prevent evaporation, plastic sheets are used to cover the samples After that, the sample will be removed from the mold after 24 hours and soaked in water at 20 ° C for curing until the test time is 7 days, 28 days and 56 days
When conducting compression testing, the compressor used is with ASTM 400 kips compression testing machine To ensure that the samples are loaded with axes, the cylinders are covered with sulfur The loading speed is 200 psi (1,4MPa) per minute until the sample is failure
Sample test for compressive strength test is performed at each test age: 7, 28 days
To avoid the loss of additives, plasticizers are washed off the mixing tank to avoid loss of additives because the amount of super-plasticizer mixed in the concrete mixture is small
Mixing Proportions and Casting Specimen
Table 3.2: Mix Proportion of specimens in trial experiment
(Source: Create based on the synthesis of studies:
ACI 522, Nguyen Van Chanh et al, 2006)
Figure 3.1 Mixing PCPC with concrete mixer
Figure 3.2 Casting specimen at Lab
Figure 3.4 Curing PCPC specimen at Lab
The process of conducting experiments has gained many valuable lessons That is understanding the characteristics of porous concrete, manufacturing processes to achieve optimal gradation in terms of strength, permeability, and other criteria of
PCPC can be considered for practical application.
RESULTS AND DISCUSSION
RESULTS
Figure 4.1 Testing PCPC at Lab
Figure 4.2 The PCPC sample is destroyed after compression
Figure 4.3 Crack of PCPC after compression
Table 4.1 Compressive strength of PCPC mix no 7-day 28-day
Figure 4.4 Compressive strength development with time
(According to ASTM C39 - Standard Test Method for Compressive Strength of Cylindrical
CT FA SG FA-SF SG-SF
Co mp res siv e streng th ( M P a)
Discussion
Figure 4.5 Testing permeability of PCPC
Table 4.2 Void ratio of PCPC – V r determine by Equation 1 of Park and Tia (chapter 3) mix no Average value
Figure 4.6 Void ratio (%) of PCPC Specimen - V r determine by Equation 1 in Chapter 3
Table 4.3 Permeability of PCPC – k determine by Equation 2 of Park and Tia (chapter 3) mix no average value
CT FA SG FA-SF SG-SF
Figure 4.7 Coefficient of Permeability (mm/s) – k determine by Equation 2 in Chapter 3
From the results shown above, porous concrete with 30% BFS (by volume of cement) possess adequate void (more than 13%) and permeability (more than 0.1cm/s) for pavement application
4.2.1 Combine slag in slurry to make porous concrete
It is better to incorporate slag in the mortar to make porous concrete better due to lower water demand to increase continuous space
In general, the strength of porous concrete depends on void ratio and permeability The higher the void ratio is, the higher the permeability is and the lower the strength is However, porous concrete with slag (SG) and slag and silica fume (SG-SF) give the highest strength, but void ratio and permeability are not the lowest
This is because of reasons as following: lower water demand of mortar with slag compared with mixture containing fly ash can be a reason Slag in the mortar decreases viscosity and yield value of mortar, a suitable value of viscosity increases the coating of mortar to aggregate and increase the ratio of continuous void as well as uniform distribution of void inside porous concrete
CT FA SG FA-SF SG-SF
4.2.2 Mortar with BFS and SF produces strength pervious concrete
When combining BFS and SF, it will produce porous concrete with the highest intensity in experimental aggregates due to the rheological properties of the dough and better consumption of Ca (OH) 2 by the pozzolanic reaction from silica
Cement hydration reaction occurs first when in concrete mixture:
Pozzolanic reaction after cement hydration
Combination of slag and silica fume in porous concrete improves strength significantly, whereas porous concrete Pozzolanic with Fly ash and silica fume decreases compressive strength compared with control porous concrete The finely spherical shape of Fly ash particle and extremely high surface area of Silica fume increase the water demand and increase the viscosity of paste Moreover, it is proposed that amount of Ca(OH)2 released from hydration products is not enough to be consumed fully by pozzolanic reaction from
Fly ash and silica fume
Thus, certain amount of fly ash and silica fume remaining in the paste created weak zone in the paste As a consequence, it decreases strength of porous concrete In contrary, adequate amount of silica fume in porous concrete with slag and silica fume consume Ca (OH) 2 fully
Also Slag itself is a cement material and its low water demand decreases viscosity of paste, which gives a mortar with optimum viscosity and yield value to coast to aggregate Thus, the void is distributed uniformly as well as compressive force is distributed uniformly through the mortar inside porous concrete This increases strength
4.2.3 Fly ash particle does not significantly enhance strength of porous concrete
Porous concrete with Fly ash particle did not considerably improve strength It can be estimated that Nano-particle with ultra-fine size cause flocculation The smaller the size of particle is, the higher the surface energy is
Therefore, if super-plasticizer is not enough to disperse flocculation, Nano-particle itself agglomerate together and they act as nucleation side to attract other particle (cement & slag of fly ash) surrounding them to hydrate (size of Fly ash is one thousand less than that of cement) A large agglomeration in the center of hydration particles was not reacted fully and remains between hydration products
This causes weak space in the paste Moreover, increase in the water demand occurs when the certain amount of water is entrapped in agglomeration, which increases viscosity of mortar and decreases the cost of mortar to aggregate As a result, agglomeration of Fly ash particle that is not dispersed well does not significantly increase the strength of porous concrete
The results show that mixing proportion with Slag gives the highest compressive strength with 25.48 MPa
TCVN 10797: 2015 requires Compress strength pavement > 9.5 MPa
In addition, Permeability coefficient of porous concrete is in the range of 1.7-2.2 mm/s
Previous research using slag as a recycled material in thermoelectric production has not shown the appropriate intensity and permeability, but this study has achieved At the same time, other indicators of porous concrete such as abrasion and durability can be added for practical applications
Therefore, PCPC using Slag, Silica fume has great potential for application in medium and small strength concrete structures such as sidewalks, parking lots.
CONCLUSION AND RECOMMENDATION
Conclusion
Firstly, combining blast furnace slag and silica fume improves the significant strength of porous concrete, retaining the appropriate void ratio and permeability
According to Vietnam Standards TCVN 10797: 2015 standard Requires compressive strength> 9.5 MPa
According to the results of this study, mixing proportion PCPC containing BFS and SF results in 28 days compressive strength test: 29.42 MPa and permeability coefficient: 1.747 mm/s
Therefore, empirical classification results in the research topic are satisfactory with the original research objectives, which can be considered for practical application
The use of silica fume as well as fly ash has a tremendous effect because it reduces dust and water pollution due to the large amount of fly ash and slag emitted from thermal power plants in Vietnam today
In addition, the application of porous concrete using slag, fly ash, silica fume will reduce the amount of cement as a binder in concrete leading to the production of PCPC as an environmentally friendly material, contributing to the sustainable development
Secondly, the rheological properties (viscosity and yield value) of mortar are important factors, affecting the continuous void, permeability and strength of porous concrete
When using SF mixed with PCPC mixture, it is necessary to add SP to increase the workability of concrete
Finally, fly ash does not significantly improve the strength of porous concrete without being evenly dispersed by super plasticity PCPC mixing proportion containing FA do not considerably increase PCPC strength but have a higher permeability coefficient than mixing proportion containing BFS and SF.
Recommendation
Challenges of Portland cement pervious concrete PCPC has the advantages that environmental friendly materials are gradually increasing in practical applications
However, there are still some limitations that occur when using PCPC, thus providing solutions to address those challenges
It is a matter of strength and durability, maintenance, most importantly congestion, construction capacity problems, restrictions on heavy vehicles and costs
Early failure affecting the industry can often be linked to a substandard mixed design The mixture is missing in the amount of cement materials in the mixture
Besides, the use of PCPC in cold climates will be hampered by the lack of a viable freeze- thaw resistant mix design So, solving these challenges requires reasonable approaches to developing design, construction and maintenance strategies
Figure 5.1: solution for designing PCPC road structure layers
PCPC pavement is only part of the entire system, although this is a very important part and will be discussed more fully later Below the pavement layer is the reservoir system, there may be some pieces including the filter layer at the top and bottom of the reservoir layer
The reservoir system may be sized to store and store certain design storm events or it may simply be a pipe to allow water to flow into the soil below or be moved out
Therefore, consideration of hydrological factors plays an important role in system design for the reservoir section, and can be separated by a geotextile layer Not all of these classes / parts are present in most applications, but each layer serves a function in such an idealized part
ACI 522.1-13 Specification for Pervious Concrete Pavement
ASTM C192, Standard Practice for Making and Curing Concrete Test
ASTM C39 / C39M - 18 Standard Test Method for Compressive Strength of Cylindrical
ASTM C618 - 19 Standard Specification for Coal Fly Ash and Raw or Calcined Natural
Pozzolan for Use in Concrete
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