Sử dụng bê tông thấm nước cho khu dân cư Pavelý ứng dụng

Sử dụng bê tông thấm nước cho khu dân cư Pavelý ứng dụng

Using Pervious Concrete for Residential Pavement Application

Le Hoang Thanh Nam 1 , Nguyen Van Chanh 2

1

Graduate Student, Department of Construction Material, University of Technology,

Assoc Lecturer, Faculty of Civil Engineering, HCM City University of Technology, Vietnam; 2

Assoc Prof PhD, Department of Construction Material, University of Technology, Vietnam

Email: 1lhtnam@gmail.com

, 2nvchanh@hcmut.edu.vn

ABSTRACT

Pervious concrete, known as a material created with a high volume of interconnected voids, is designed to trap water and allow it to percolate through It helps not only to manage water runoff in a sustainable way but also to remove some harsh chemicals and pollutants before the water returns the ecosystem This paper presents method of producing pervious concrete based on raw materials almost similar to producing normal concrete but having little or no fine aggregate Experimental results show that, the compressive strength can reach 4.1 – 8.6 MPa when the void content is in the range of 22.3 – 33.6% and water permeability is about 0.0141 – 0.0223m/s Construction method of residential road is also presented

KEYWORDS: pervious concrete, interconnected voids, water permeability, mechanical

properties

1 INTRODUCTION

Nowadays, urbanization leads to a lot of ground surface is concreted over It also means that there are more and more impermeable surface areas created These areas make rain water hard to go into the ground below It could be one of the factors contributing to reduce underground water level It also keeps storm-water runoff volume on the surface, resulting in water flooding

Using permeable materials like pervious concrete to construct road, parking lot, sidewalk, etc is considered as a sustainable way to solve this problem in recent decades all over the world Due to the permeability requirement, pervious concrete is typically designed with high void content in the range of 20 – 30% Pervious concrete consists of cementitious material, water, aggregate and often admixtures This type of concrete is usually produced by using a much narrower distribution of coarse aggregates, and less or no fine aggregate compared with traditional concrete This material has two phases, includes solid and void phase Solid phase consists of coarse aggregate covered and bonded by cementitious mortar And void phase consists of voids which are at least partially connected For this reason, the pervious concrete not only has significantly increased permeability to allow water penetration and filtration but also lowers strength and potentially lowers durability

In this paper, pervious concrete were designed with three dimension types of coarse aggregate as well as various ratios of aggregate to cement Compressive strength, splitting tensile strength, modulus of elasticity, void content, and water permeability were tested The effects of void contents on other properties of pervious concrete were also surveyed by means

of ratio of aggregate to cement Designing of structure and construction method of pervious

concrete pavement for residential road was also presented The following sections describe the detailed experiments, test results, and major findings

2 MATERIALS AND METHODS

2.1 Materials

Portland cement was used in all mixes

Crushed stone which passed the 19.0mm sieve but retained on the 4.75mm sieve was used

as coarse aggregate They are separated into three groups as shown in table 1 below

Table 1.Groups of coarse aggregate

Group of coarse aggregate

Retaining sieve (mm)

Passing sieve (mm)

2.2 Mix proportions

Mix proportions are designed based on the specified ratios of coarse aggregate to cement; ratio of water to cement and retarding admixture to cement are fixed as 0.33 and 0.1 respectively Because the hardening time of pervious concrete is relatively short, it is necessary to use retarding admixtures in mixture Experimental samples’ mix proportions are shown in Table 2

Table 2.Mix proportions

Group of

Coarse

Aggregate

Mix

Cement (C) (kg/m 3 )

Water (W) (lit/m 3 )

Coarse Aggregate (A) (kg/m 3 )

A/C W/C R.A (*) /C

A (Dmin =

4.75mm)

B (Dmin =

9.5mm)

C (Dmin =

12.5mm)

(*)

Retarding admixture

2.3 Specimen preparation

The mixing procedure has to be considered to increase the bond between cement paste and aggregate First of all, a small amount of cement (5 – 10%) was mixed with aggregate in dry state for 1 – 2 minutes Then, water and the remaining cement were added to the mixer The mixture was then mixed for about 2 minutes, rested for 2 minutes, and then mixed for 2

Specimens were placed in cylindrical molds for splitting tensile strength, compressive

strength, elastic modulus, and water permeability tests (Figure 1)

2.4 Water permeability test

2.4.1 Testing apparatus

Water permeability of pervious concrete samples was determined by an apparatus described as Figure 2 below It has a plastic pipe called “penetration pipe” with 95mm in inner diameter and 250mm in length The top part of penetration pipe is 150mm long, encloses the specimen This pipe is connected with a drainage pipe of 49 mm in diameter through a valve of also 49 mm in diameter according to the principle of communicating vessels Top of drainage pipe is 10mm higher than top of the installed specimen The apparatus also contains a pipe with scale division from 0 to 300mm used to observe water level during experiment process

2.4.2 Procedure of testing

Cylindrical specimen of pervious concrete with [diameter] x [length] = 95mm x 150mm is wrapped by a latex coat before placed in penetration pipe Soak specimens for 24 hours in water in order to exclude the air in holes of pervious concrete Close valve then pour water into division pipe so that the water level is at 300mm When the valve is opened, water penetrates through the concrete specimen and goes to drainage pipe according to the principle

of communicating vessels Determine the time t (seconds) of changing water levels from 290

mm high (h1) to 70 mm high (h2) The experiment is repeated three times; three values are determined including t1, t2, t3 respectively Get the average time over 3 period values

Figure 1 Produced pervious concrete specimens Figure 2 Water permeability test setup 2.4.3 Calculating

Coefficient of permeability (K) is calculated by Darcy's law:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

=

2 1 2

1. lg

h

h t A

L A K

Where: A1 is cross sectional area of the standpipe; A2 is cross sectional area of specimen; L is the length of specimen; t is time in seconds from h1 = 290mm to h2 = 70mm

3 RESULTS AND DISCUSSION

Test results of physical and mechanical properties of mix samples are summarized in table 3 below

Table 3.Summary of test results

Mix

Void content (%)

Permeability (m/s)

Compressive strength (MPa)

Splitting tensile strength (MPa)

Elastic modulus (MPa)

3.1 Void content of pervious concrete

Surveying all three groups of mix proportion corresponding to three groups of coarse aggregate, it has been shown that the void content increases when the ratios of aggregate – cement increases from 4.5 to 6.0 It was also found that the larger sizes of coarse aggregate, the higher void content of pervious concrete (Figure 3) The minimum and maximum void content of these samples are 22.3% and 33.6%, respectively

When types of larger coarse aggregate are used, holes between them increase in size It causes a higher void content of pervious concrete

When the ratio of coarse aggregate/cement increases, it means that the amount of cementitious material reduces This amount is so small that it’s just enough to cover aggregate particles and create connection among them It also means that there is very little cement paste filling the gaps among particles, results in a high void content of pervious concrete However, the increasing of void content is limited when there is too little cement paste in the mixture There is no cementitious material to fill the gaps and almost not enough to connect particles It causes not only the reducing in strength of concrete but also the difficulty in mixing process

3.2 Permeability of pervious concrete

The most important property of pervious concrete is the permeability Experimental testing shows that permeability of specimens varies in the range of 0.0141 to 0.0223m/s It’s also influenced by aggregate particles’ size and ratio of coarse aggregate/cement According to test results, coefficient of permeability is higher when Dmin of aggregate particles is higher in the range of 4.75 to 12.5mm This coefficient also increases when the ratio of coarse aggregate to cement varies from 4.5 to 6.0 It’s clear to realize that the higher void content leads to the higher permeability of concrete

5

10

15

20

25

30

35

V

o

 c

o

te

n

t (

%

)

Ratio of coarse aggregate/cement

D.min = 4.75mm D.min = 9.5mm D.min = 12.5mm

0.000 0.005 0.010 0.015 0.020 0.025

C e ff ic ie

t  o e rm e ili ty  ( m /s )

Ratio of coarse aggregate/cement

D.min = 4.75mm D.min = 9.5mm D.min = 12.5mm

Figure 3 Relationship between ratio of

coarse aggregate to cement and void

content

Figure 4 Relationship between ratio of coarse aggregate to cement and coefficient

of permeability 3.3 Compressive strength of pervious concrete

Compressive strength depends on many parameters but most of them relate to the factor of void content Thus, ratio of coarse aggregate/cement has significant effects to compressive strength as though the factor directly affects void content (Figure 5) Test results show that the compressive strength of specimens after 28 days varies in the range of 4.1 MPa to 8.6 MPa

0

1

2

3

4

5

6

7

8

9

10

C

o

m

p

ss

iv

 s

tr

e

gt

h

 (M

P

Ratio of coarse aggregate/cement

3 days

7 days

28 days

Dmin= 4.75mm

0 1 2 3 4 5 6 7 8

C m p ss iv  s tr e gt h  ( M P )

Ratio of coarse aggregate/cement

3 days

7 days

28 days

Dmin= 9.5mm

0 1 2 3 4 5 6 7 8

C m p ss iv  s tr e g  ( M P

Ratio of coarse aggregate/cement

3 days

7 days

28 days

D min = 12.5mm

Figure 5 Relationship between ratio of coarse aggregate to cement and compressive

strength with D min = 4.75mm; 9.5mm; and 12.5mm respectively

When coarse aggregate/cement ratio increases from 4.5 to 6.0, the compressive strength of all three groups of aggregate as well as all days of age decreases High ratio of coarse aggregate/cement leads to little amount of cement It causes the structure of the hardened cement paste to weaken and thus the concrete strength significantly reduces However, the

coarse aggregate/cement ratio has to be kept at relatively high levels due to maintaining the ability of water permeability as discussed above

3.4 Splitting tensile strength and elastic modulus of pervious concrete

Splitting tensile strength is in the range of 0.94 – 3.42 MPa (Figure 6) and elastic modulus varies from 18936 to 40712 MPa (Figure 7) It can be seen that two mechanical properties of pervious concrete are also significantly influenced by coarse aggregate/cement ratio Both of them reduce when the ratio mentioned above increases from 4.5 to 6.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Sp

lit

ti

n

 t

e

si

le

 s

tr

e

g

 (

M

P

)

Ratio of coarse aggregate/cement

D.min = 4.75mm D.min = 9.5mm D.min = 12.5mm

0 5000 10000 15000 20000 25000 30000 35000 40000 45000

El st  m o u

s  (M P )

Ratio of coarse aggregate/cement

D.min = 4.75mm D.min = 9.5mm D.min = 12.5mm

Figure 6 Relationship between ratio of

coarse aggregate to cement and splitting

tensile strength

Figure 7 Relationship between ratio of coarse aggregate to cement and elastic

modulus

4 DESIGN AND CONSTRUCTION RESIDENTIAL ROAD

4.1 Design structure of road

The first layer (from bottom up) is soil base under road structure The top-50cm of this layer must be compacted with compacting factor greater than 0.92 The second layer is non-woven geotextile The third layer is constructed by gravel Its depth is about 30 – 50cm The fourth layer’s depth is 2 – 5cm, made of sand The top layer is made of pervious concrete

Figure 8 Structure of pervious concrete pavement

4.2 Method of construction road

Construction process contains three stages: construction base, foundation, and pervious concrete pavement

First, cut the top layer of the original ground to designed height Compact soil according to ASTM D1557 or AASHTO T180 until compacting factor is greater than 0.92 In the case of embanking, road pavement base has to be embanked layer by layer; each layer’s depth is not exceeding 20cm

Overlay the road base by non-woven geotextile Place a layer of 30 – 50cm by gravel of 10 – 20mm diameter After that, place a sand layer of 2 – 5cm to make a flat surface

Before casting pervious concrete, formwork must be erected and fixed on road foundation

and transported to the site by concrete truck Concrete mixture is casted onto road foundation and cured by watering

5 CONCLUSION

Pervious concrete has a great ability to allow water to percolate through Permeability of this material can reach the value of 0.0141 – 0.0223m/s while the compressive strength is of 4.1 – 8.6 MPa It allows using pervious concrete for residential pavement construction

The construction of residential road made of pervious concrete pavement is not far different from of normal concrete pavement This material is not only suitable for the process

of urbanization but also helpful for drainage systems

REFERENCES

[1] Nguyen Van Chanh, “Study of pervious concrete for civil construction, a sustainable

material”, Proceeding of the 2 nd Practicing Science and Technology Conference, Vietnam

Academy of Science and Technology, 2006

[2] Wang, K, et al, "Development of Mix Proportion for Functional and Durable Pervious

Concrete", Proceedings of the 2006 Concrete Technology Forum, Nashville, TN, National

Ready Mix Concrete Association, 2006

[3] Mahboub, K.C., et al, “Pervious Concrete: Compaction and Aggregate Gradation”, ACI

Materials Journal, Vol 106, No 6, pp 523-528, Nov 2009

[4] Bentz, D P., “Virtual Pervious Concrete: Microstructure, Percolation, and Permeability”,

ACI Materials Journal, Vol 105, No 3, pp 297-301, May 2008

[5] Vietnam Branch Standard 22TCN 223-1995, “Rigid pavement – Design standard”