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
Porous concrete, as defined by the National Ready Mixed Concrete Association (NRMCA), is a high porosity concrete ideal for flat surface applications, enabling rainwater and other sources to permeate through it This characteristic helps manage water flow and recharge groundwater levels Also known as non-fines concrete, it is composed of Portland cement, coarse aggregates, and water, typically containing little to no sand or additives.
The draining water PCP offers numerous advantages, including enhanced safety during rainy conditions, reduced noise levels, and excellent anti-slip performance This type of pavement prevents water accumulation, splash, and spray, significantly improving driving safety in wet weather Its effectiveness has led to widespread adoption in Western Europe.
US and Japan and so on
Porous concrete serves as an effective pavement material that allows rainwater to penetrate at the source, enhancing driving safety and reducing noise levels Additionally, it mitigates the heat effects of traffic in urban areas, promoting a more sustainable environment This innovative solution not only addresses marketing challenges but also supports sustainable development initiatives.
Evaluating the environmental impact of porous concrete compared to conventional concrete reveals distinct differences Porous pavement allows air, water, and temperature to permeate various environmental layers, facilitating unique storage, handling, and flow processes Consequently, porous concrete is recognized as an eco-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 is characterized by key indicators such as strength, permeability, abrasion resistance, and surface texture This thesis primarily examines two critical factors: the strength and permeability of Pervious Concrete Pavement (PCP).
This study utilizes a widely used polycarboxylate-based super plasticizer, SP8P, commonly found in Japan This admixture enhances the workability and slump of concrete while also prolonging the setting time of both cement and concrete.
At Komaba Lab, an experimental process was conducted to create PCP samples, focusing on the design and testing of concrete's compressive strength in accordance with ACI 522 standards Additionally, the permeability of the PCP was evaluated using Park and Tia’s Equation (2004).
Incorporating materials like Blast Furnace Slag (BFS) and Fly Ash (FA) as partial cement replacements, along with additives such as Super Plasticizer (SP) and Silica Fume (SF), can lead to the development of an optimal concrete mixture This innovative approach ensures that the resulting concrete possesses adequate strength and permeability for practical applications.
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
Research by Nguyen Van Chanh highlights that pervious concrete features a continuous pore structure with a magnetic porosity ranging from 15-35% This type of concrete shares a similar composition with standard concrete but utilizes coarse aggregates of uniform grain size and contains minimal to no sand.
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
The water-to-cement (W/C) ratio for porous concrete ranges from 0.25 to 0.45 In contrast to traditional concrete, porous concrete contains a lower cement content than the volume of pores present between the aggregate particles.
Increasing the strength of cement mortar enhances the overall strength of porous concrete, making it essential to closely monitor water content.
Properly balancing water in the concrete mixture is essential for achieving the desired properties, preventing the mortar from sinking to the bottom layer and filling the pores, which can lead to drainage issues in porous concrete.
Pervious concrete mix designs in the United States consist of cement and coarse aggregates ranging from 2.54 cm to No 4 sieve sizes These mixes are categorized based on a water-to-cement (W/C) ratio that typically falls between 0.25 and 0.43.
The 28-day compressive strength of porous concrete varies between 7 MPa and 24 MPa, with void rates between 14% and 31% and permeability velocities ranging from 2 to 6 cm/min In contrast, conventional concrete typically exhibits compressive strengths between 28 MPa and 32 MPa (3,500 to 4,000 psi), indicating that porous concrete falls short of the 3,000 psi threshold.
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)
Concrete pavement exhibits lower strength compared to traditional concrete, which restricts its use primarily to low-intensity applications Consequently, PCPC is suitable for areas such as parking lots, shoulder lanes, and light traffic roads, but it is not recommended for highway construction.
A comprehensive long-term study is essential to identify the ideal mixing ratio for porous concrete pavements, aiming to improve their strength while maintaining suitable permeability for use in highway surfaces.
Nader Ghafoori and Shivaji Dutta found that both sealed and wet curing conditions produce similar effects on strength development in concrete Additionally, the increase in compaction energy does not influence strength gains under either curing method However, it was observed that the strength of no-fine concrete improves with higher compaction energy.
The presence of interconnected voids in permeable concrete enhances water movement Increased porosity results in lower strength, while decreased porosity leads to greater strength in the porous concrete structure (Ferguson, 2005).
METHODOLOGY AND EXPERIMENT
Methodology
Topics using experimental methods to research The steps for conducting the study include:
The grading calculation involves the use of cement, coarse aggregates, fine aggregates with fly ash (FA), and blast furnace slag (BFS) as a partial replacement for cement, along with superplasticizer (SP) and silica fume (SF) additives, following the ACI 522 standard and building upon previous research findings Subsequently, samples are cast and tested for the strength and permeability of permeable concrete pavements (PCPC).
Experimental procedure
This research employs four key tests to evaluate the properties of pervious concrete mix: unconfined compressive strength, flexural strength, void ratio, and permeability The methods and formulas used for these characterization tests are detailed below.
3.2.1 Compressive and flexural strength test
The slump of fresh concrete is evaluated using the standard cone test per ASTM C143 Compressive strength is assessed in accordance with ASTM C39, while flexural strength testing follows ASTM C78, utilizing a simple beam with third-point loading For compressive strength tests, cylinder specimens measuring 10 cm in diameter and 20 cm in length are employed, whereas prismatic samples measuring 10x10x40 cm are used for flexural strength evaluation.
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, encased in rubber and secured with adjustable tube clamps, are cylindrical with a diameter of 10 cm and a height of 20 cm The average permeability coefficient (k) is calculated using the Das equation (1998).
The coefficient of permeability (k), measured in cm/sec, is calculated using the area of the standpipe (a) in cm² and the height of the sample (L) in cm The formula also incorporates the area of the sample (A) in cm² and the time (t) it takes for the water level to drop from the initial height (h₀) to the final height (hₜ) in seconds, where h₀ represents the initial water height in the burette at time t = 0, and hₜ denotes the water height at time t.
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 from Japan, is a dark brown aqueous solution containing 42% solids and a density of 1.2 It is used to enhance the dispersion of nanoparticles and silica in binders, improving the 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 R5210
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
Burning coal in power plants generates by-products, primarily fly ash A summary of the properties and chemical composition of various types of fly ash has been presented by Helmuth (Mindes and Young).
Fly ash is classified into two types based on its chemical composition: type F and type C Type F contains a lower amount of calcium oxide (CaO), resulting in reduced cementitious properties, while type C has a higher CaO content, enhancing its cement properties and making it less toxic compared to type F fly ash.
Fly ash particles are spherical and primarily composed of SiO2, Al2O3, and Fe2O3 Incorporating fly ash into concrete mixtures enhances workability and reduces hydration, offering significant benefits for construction projects.
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
In the mixing process, dry ingredients such as cement, fly ash or slag, coarse aggregate, and sand are blended in a mixer for 30 seconds Following this, a mixture of water, superplasticizer (SP), and silica fume (SF) is gradually added and thoroughly combined.
1 minute, Hold for 1 minute before final mixing for 1 minute
Porous concrete mixing involves combining silica fume, cement powder, fly ash or slag, and silica fume This mixture is blended in a planetary mixer under dry conditions for a duration of three minutes.
In the process of mixing, raw aggregate and sand are first introduced into the rotary drum mixer Following this, the dry mixture is combined for 30 seconds Next, a liquid mixture of additives is gradually added and mixed for one minute, with a pause of one minute before concluding with an additional minute of mixing.
Fresh concrete is poured into cylindrical molds and prisms designated for specific tests Each cylinder is compacted by making 25 pokes with 10 mm diameter skewers, applied in three layers To prevent pitting on the concrete sample's surface, the outer mold is lightly tapped 15 times with a mallet after each layer is added.
To create a prismatic beam pattern measuring 10x10x40 cm, begin by filling the mold with concrete Flex the mold 30 times using a round head with a 16mm diameter, ensuring to flex once for every 14 cm² of the upper surface area Next, apply external vibration to each of the four corners of the mold with a hard shaft vibrator for approximately 3 seconds per 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
To create a prismatic beam pattern, two samples are placed in a steel formwork mold, which is secured with 30 clamps for each layer of concrete After adding two layers of concrete, a vibrator is applied to each of the eight corners for 10 seconds following each layer.
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
Conducting experiments on porous concrete has yielded valuable insights into its characteristics and manufacturing processes These findings are essential for achieving optimal gradation in strength, permeability, and other critical criteria, making them applicable for practical use in construction and engineering projects.
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 Concrete Specimens)
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
The strength of porous concrete is primarily influenced by its void ratio and permeability; typically, a higher void ratio leads to increased permeability and reduced strength However, the combination of slag (SG) and slag with silica fume (SG-SF) results in superior strength, even though these mixtures do not exhibit the lowest void ratios or permeability levels.
The lower water demand of slag-based mortar compared to fly ash mixtures contributes to its effectiveness Slag reduces the viscosity and yield value of the mortar, leading to improved coating on aggregates This results in a higher ratio of continuous voids and a more uniform distribution of voids within porous concrete.
CT FA SG FA-SF SG-SF
4.2.2 Mortar with BFS and SF produces strength pervious concrete
Combining BFS and SF results in the production of high-intensity porous concrete, attributed to the favorable rheological properties of the mixture and enhanced consumption of Ca(OH)2 through the pozzolanic reaction with silica.
Cement hydration reaction occurs first when in concrete mixture:
Pozzolanic reaction after cement hydration
The combination of slag and silica fume in porous concrete significantly enhances its strength In contrast, the use of Fly ash and silica fume in porous concrete reduces compressive strength compared to standard porous concrete The spherical shape of Fly ash particles and the high surface area of silica fume lead to increased water demand and higher paste viscosity Additionally, it is suggested that the amount of Ca(OH)2 released during hydration is insufficient to be fully utilized by the pozzolanic reactions of Fly ash and silica fume.
The presence of fly ash and silica fume in concrete paste can create weak zones, leading to a reduction in the strength of porous concrete Conversely, an optimal amount of silica fume in combination with slag effectively consumes Ca(OH)₂, enhancing the overall strength and durability of the porous concrete.
Slag serves as a cement material that reduces water demand, resulting in lower viscosity of the paste This enhancement leads to a mortar with optimal viscosity and yield value, allowing for better bonding with aggregates Consequently, the uniform distribution of voids and compressive forces within the mortar enhances the strength of porous concrete.
4.2.3 Fly ash particle does not significantly enhance strength of porous concrete
Porous concrete incorporating fly ash particles did not show a significant enhancement in strength It is suggested that nano-particles with ultra-fine dimensions may lead to flocculation, indicating that smaller particle sizes result in increased surface energy.
If super-plasticizers fail to effectively disperse flocculation, nanoparticles can agglomerate, acting as nucleation sites that attract surrounding particles such as cement and slag from fly ash Given that the size of fly ash particles is significantly smaller—about one-thousandth the size of cement—this agglomeration can lead to incomplete reactions, leaving large clusters of unreacted particles within the hydration products.
The presence of weak spaces in the paste leads to increased water demand due to water being trapped in agglomerations, which raises the viscosity of the mortar and reduces its cost relative to aggregate Consequently, poorly dispersed agglomerations of fly ash particles do not significantly enhance 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
Recent studies have highlighted the limitations of using slag as a recycled material in thermoelectric production, particularly in terms of intensity and permeability However, this research successfully addresses these issues, demonstrating improved performance Additionally, it suggests that other key indicators of porous concrete, such as abrasion resistance and durability, can be incorporated to enhance 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 incorporation of silica fume and fly ash significantly mitigates dust and water pollution in Vietnam, addressing the substantial emissions of fly ash and slag from thermal power plants.
The use of porous concrete incorporating slag, fly ash, and silica fume decreases the reliance on cement as a binder, resulting in the creation of PCPC, an eco-friendly material that supports 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
Fly ash does not notably enhance the strength of porous concrete unless it is evenly distributed through superplasticizers The mixing proportions of porous concrete with fly ash do not significantly boost strength compared to those with blast furnace slag (BFS) and silica fume (SF), but they exhibit a higher permeability coefficient.
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
The effectiveness of PCPC in cold climates is limited due to the absence of a suitable freeze-thaw resistant mix design Addressing these challenges necessitates the development of practical design, construction, and maintenance strategies.
Figure 5.1: solution for designing PCPC road structure layers
The PCPC pavement is a crucial component of the overall system, warranting further discussion Beneath the pavement layer lies the reservoir system, which may consist of various elements, including filter layers positioned at both the top and bottom of the reservoir.
The reservoir system can be designed to accommodate specific storm events for effective water storage, or it may function merely as a conduit to facilitate water infiltration into the ground or its removal.
In reservoir system design, it is crucial to consider hydrological factors, which can be effectively separated by a geotextile layer While not all classes or components may be present in every application, each layer fulfills a specific function within this idealized framework.
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 Concrete Specimens
ASTM C618 - 19 Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete
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Elsayed (2011) “Influence of Silica Fume, Fly Ash, Super Pozz and High Slag Cement on Water Permeability and Strength of Concrete”, Jordan Journal of Civil Engineering, Volume 5, No 2
Ferguson, B K (2005) Porous Pavements Taylor and Francis Group New York https://www.researchgate.net/publication/228841934
Husain N Hamdulay, Roshni J John, and D R Suroshe (2015) conducted a study published in the International Journal of Innovation Research in Science Engineering and Technology, Volume 4, Issue 8, focusing on the impact of aggregate grading and cementitious by-products on the performance of pervious concrete Their research, spanning pages 6890 to 6897, highlights the significance of these factors in enhancing the durability and efficiency of pervious concrete applications.
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