Chapter III

CHAPTER III

MATERIALS AND METHODS

3.1 General

This chapter deals with the materials used and methods adopted to conduct study on the

characteristics of pervious concrete.

3.2 Material used

3.2.1 Cement

Cement is a fine, soft, powdery-type substance made from a mixture of elements that are found in

natural materials such as limestone, clay, sand or shale. Cement is usually of grey colour. White cement

can also be found but it is usually more expensive than gray cement. Cement is a binding substance with

adhesive and cohesive properties which sets and hardens independently and binds other materials into a

compact-solid. When cement is mixed with water, it can bind sand and gravel into a hard solid mass

called concrete. When cement is mixed with water, lime and sand it forms mortar.  The cement contains

two basic ingredients namely argillaceous and calcareous. Ordinary Portland Cement (OPC) is the most

important type of cement. OPC is classified into three grades, namely 33 grade, 43 grade and 53 grade

depending upon the compressive strength of cement at 28 days. . Portland cement concrete is foremost

used among the construction materials around the world because it is very versatile, economical and

widespread availability of its constituents.

Shree Ultra 43 grade OPC was used in this study. It was fresh and free from any lumps. The

properties of cement were determined and are given in chapter IV.

Shree Ultra OPC

3.2.2 Aggregate

Aggregates are the most mined materials in the world. They are a component of composite

materials such as concrete and asphalt concrete. Generally, aggregates occupy 70% to 80% of the volume

of concrete and have an important influence on its properties. The aggregate serves as dimensional

stability and reinforcement to add strength to the overall composite material. They are granular materials,

derived from natural rock (crushed stone, or natural gravels). Due to the relatively high hydraulic

conductivity value as compared to most soils, aggregates are widely used in drainage applications . For a

good concrete mix, aggregates need to be clean, hard, strong particles free of absorbed chemicals or

coatings of clay and other fine materials that could cause the deterioration of concrete. Soft and porous

rock can limit strength and wear resistance and sometimes it may also break down during mixing and

adversely affect workability by increasing the amount of fines. Using washed aggregates normally gives a

more consistent product. The shape and particle size distribution of the aggregate is very important and

affects the packing and voids content. Single size aggregates and/or a gap in the grading between coarse

and fine aggregates are used in some mix designs.

3.2.2.1 Coarse aggregate

Coarse aggregates are particles greater than 4.75mm, but generally range between 9.5mm to

40mm in diameter and contain only that much of fine material as is permitted by the specifications. The

graded coarse aggregate is described by its nominal size i.e. 40 mm, 20 mm, 16 mm, 12.5mm and 10 mm.

They can either be from primary source (rock or gravel), secondary source (by-products of extractive

operations) or recycled sources (used concrete). The aggregates derive many of their properties such as

chemical and mineral composition, specific gravity, hardness, strength, pore structure and colour from the

parent rocks. All these properties may have considerable effect on the quality of concrete. The particle

size distribution and the shape of coarse aggregate directly influence the flow and passing ability of

pervious concrete and its paste demand. More the spherical shape aggregates in mix, less they are likely

to cause blocking and greater the flow because of reduced internal friction. Crushed stone aggregate

(locally available) of nominal size 40mm, 20 mm and 10 mm were used in the various proportion

throughout the experimental study. The aggregates were washed to remove dust and dirt and were dried to

surface dry condition. The properties of coarse aggregates such as specific gravity, bulk density and water

abroption were determined and are given in chapter IV.

10mm 20mm 40mm

3.2.2.2 Fine aggregate

No fine aggregates have been used.

3.2.3 Water

Fresh and clean tap water was used for casting the specimens in the present study. The water was

relatively free from organic matter, silt, oil, sugar, chloride and acidic material as per Indian standard.

3.3 Mix Proportion and Mix design method

For mix proportion selection three trial mixes with different cement - aggregates ratio (i.e. 1:4,

1:6, 1:8) were selected keeping w/c ratio constant. All three trials were performed on the same aggregates

proportion of 10mm, 20mm and 40mm (i.e. 1:1:2) respectively. After 28 days compressive strength and

porosity of mixes were calculated and from the observed data, 1:8 gives best results and prove to be

economical as compared to other two mixes because as 1:4 have more cement slurry which more strength

then other two but reduces the pores and which will affect the permeability and 1:6 gives average result as

compare to 1:8.

The basic steps involved in the concrete mix design can be summarized as follows:

i) Based on the literature the mean target strength is estimated

ii) The water cement ratio is selected for the mean target strength and checked for the requirements

of durability.

iii) The water content for the required workability is determined.

iv) The cement content to be determined from the trial mix ratio and water content obtained in step

(ii) and (iii) respectively and is checked for the water requirements.

v) The relative proportion of coarse aggregates is selected from the characteristic of coarse

aggregate.

vi) The trial mix proportions are determined.

vii) The trial mixes are tested for verifying the compressive strength and suitable adjustments are

made to arrive at the final mix composition.

3.4 METHODS

The procedure of methods used for testing cement, coarse aggregates, and concrete are given

below:

3.4.1 Specific gravity

The specific gravity is a dimensionless unit defined as the ratio of the density (mass of a unit

volume) of a substance to the density (mass of the same unit volume) of a reference substance. The

reference substance is water for liquids or air for gases. The specific gravity of the solid is the ratio of its

weight in air to the difference between its weight in air and its weight immersed in water.

3.4.2 Bulk Density

Unit weight (bulk density) is the weight of unit volume of aggregates, usually stated in Kg per

litre. It was calculated to know the estimating quantities of material when batching is done on a

volumetric basis. Bulk density of aggregates is the ratio of weight of loose aggregates and the volume of

container.

Loose Bulk density=(wt .of container+loose aggregates )−(wt of empty container )

volume of container

3.4.3 Fineness of cement

i) Weigh accurately 100gm of cement in rice plate.

ii) Place it on standard IS 90 micron sieve breaking down any air-set lumps in the cement sample

with fingers.

iii) Continuously sieve the sample by holding the sieve in both the hands. Sieve with a gentle wrist

motion for period of 15 minutes.

iv) Weigh the residue after 15 minutes of sieving.

v) Repeat the procedure for two more such samples.

Fineness of cement = (weight of residue / weight of sample) X 100 = ........%

Fineness of Cement

3.4.4 Standard consistency of cement

The standard consistency of a cement paste is defined as that consistency which will permit a

vicat plunger having 10 mm diameter and 50 mm length to penetrate to a depth of 33-35 mm from the top

of the mould.

i) Weigh approximately 400 gm of cement and mix it with a weighed quantity of water. The time

of gauging should be between 3 to 5 minutes.

ii) Fill the vicat mould with paste and level it with a trowel.

iii) Lower the plunger gently till it touches the cement surface.

iv) Release the plunger allowing it to sink into the paste.

v) Note the reading on the gauge.

vi) Repeat the above procedure taking fresh samples of cement and different quantities of water

until the reading on the gauge is 5 mm to 7 mm.

Vicat Apparatus

3.4.5 Determination of Initial and Final Setting time

i) Take 400 gm of cement and prepare a neat cement paste with 0.85P of water by weight of

cement where P is standard consistency of cement as found earlier.

ii) Gauge time is kept between 3 to 5 minutes.

iii) Fill the vicat mould with cement and smoothen the surface of the paste making it level with the

top of the mould. The cement block thus prepared is known as test block.

iv) For initial setting time place the test block confined in the mould and resting on non porous plate

under the rod bearing needle, lower the needle gently in contact with the surface of the test

block.

v) In the beginning the needle completely pierces the test block. Repeat this procedure until the

needle fails to pierce the block for about 5 mm measured from the bottom of the mould.

vi) The period elapsing between the time when water is added to the time at which the needle fails

to pierce the test block by about 5 mm is the initial setting time.

vii) For determining the final setting time, replace the needle of vicat apparatus by the needle with an

annular attachment.

viii) The cement is considered finally set when upon applying the final setting needle gently to the

surface of the block, the needle makes an impression thereon, while the attachment fails to do so.

The period elapsing between the time when water is added to the cement and the time at which

the needle makes an impression on the surface of the test block while the attachment fails to do

so shall be the final setting time.

3.4.6 Determination of compressive strength of cement

Compressive strength of cement is determined from cubes of 70.6 mm X 70.6 mm X 70.6 mm in

size, made of cement mortar with one part of cement and three parts of standard sand.

The quantity of materials for each cube taken as follows:-

Cement : 200 gm

Standard sand : 600 gm

Water = (P/4+3.0) percent weight of cement and sand

Where P is the percentage of water required to produce a paste of standard consistency determined as

described in IS: 4031 (part 4) -1988.

Procedure:

i) Gauge a mixture of cement and standard sand in the proportion of 1:3 by weight using (P/4+3.0)

percent of water required to produce a paste of standard consistency.

ii) Fill the cube moulds by compacting it for two minutes on a vibrating machine.

iii) Smoothen the top surface of the cubes with flat side of trowel.

iv) Immediately upon completion of moulding, place the cube moulds in an atmosphere of 27 C±⁰

2°C.

v) After 24 hours, remove the specimen from the moulds and keep them in water for curing till

testing.

vi) Test the cubes at 7 and 28 days age in the compression testing machine.

vii) Report the average compressive strength in MPa.

Tester Cubes Compression testing machine

3.4.7 Workability of Pervious Concrete

Workability is that property of freshly mixed concrete or mortar which determines the ease and

homogeneity with which it can be mixed, placed, consolidated, and finished. Workability is not just based

on the properties of the concrete, but also on the nature of the application. The strength and durability of

hardened concrete, in addition to labour costs, depend on concrete having appropriate workability.

Workability test methods have been classified in terms of the type of flow produced during the

test. Commonly used test methods are:-

1. Slump Flow Test

2. Confined Flow Test

3. Compaction Factor Test

4. Ring Penetration Test

5. Cone Penetration Test

6. Vee Bee Consistometer Test

7. Flow Table Test

8. Inverted Slump Cone Test

Compaction factor test was used for finding workability of freshly prepared pervious concrete in

laboratory in this research. The apparatus for compaction factor test consist of a rigid frame that supports

two conical hoppers vertically aligned above each other and mounted above a cylinder. A freshly mix

concrete was filled in the top hopper but not compacted. The door on the bottom of the top hopper was

opened and the concrete was allowed to drop into the lower hopper. Once all of the concrete had fallen

from the top hopper, the door on the lower hopper was opened to allow the concrete to fall to the bottom

cylinder. The excess concrete was carefully struck off the top of the cylinder and the mass of the concrete

in the cylinder was recorded. This mass was compared to the mass of fully compacted concrete in the

same cylinder achieved with hand rodding or vibration. The compaction factor is defined as the ratio of

the mass of the concrete compacted in the compaction factor apparatus to the mass of the fully compacted

concrete.

Interpretation of Compaction Factor Results ( )

Degree of Workability

Slump(mm)

Compaction FactorApplicationsSmall

ApparatusLarge

ApparatusVery Low 0-25 0.78 0.80 Vibrated concrete in roads or other

large sections.

Low 25-50 0.85 0.87Mass concrete foundation without

vibration. Simple reinforced section with vibration

Medium 50-100 0.92 0.935Normal reinforced work without vibration and heavily reinforced

section with vibration.

High 100-180 0.95 0.96Section with congested

reinforcement. Not normally suitable for vibration.

3.4.8 Compressive strength of Pervious Concrete

The quantities of cement, coarse aggregates (40mm, 20 mm and 10 mm) and water for each batch

were weighed separately. All three sizes of aggregates were placed in the mixer and mixed for 2 minutes.

The cement was mixed dry with the aggregates in mixer. Water was added to the mix and then mixed

thoroughly for 3 to 4 minutes in mixer.

Cube moulds were cleaned and oil was applied on its inner surface. The mould was filled 1/ 3

with the concrete and manual compaction was done with 25 strokes of tamping rod. Again the process

was repeated 2 more times for completely filling the mould. The surface of the concrete was finished

level with the top of the mould using trowel. The finished specimens were left to harden in air for 24

hours. The specimens were removed from the moulds after 24 hours of casting and were placed in the

water tank, filled with potable water in the laboratory.

Specimens were taken out from the curing tank at the ages of 7, 14 and 28 days. Surface water

was wiped off and specimens were immediately tested on removal from the curing tank. The load was

applied gradually without shock till the failure of the specimen occur and thus the compressive strength of

concrete cubes was found.

3.4.9 Void ratio of Pervious Concrete

Void ratio (e) of any concrete specimen is defined as the ratio of volume of voids (Vv) to the

volume of solids (Vs). Void Ratio (e) is also related to porosity (n). Strength of the concrete specimen can

be judged from its void ratio. As higher the void ratio lower will be the strength and vice versa. Void ratio

(e) is found by simple experiment performed in a laboratory by submerging the 28 days cured cube in the

bucket filled with water. A hole was made in the bucket to maintain the constant level of water. The cube

was submerged in the bucket and the water level in the bucket will rise. The cube was allowed to sit

saturate. When air bubbles disappear, the hole in the bucket as opened and water was allowed to escape

from the bucket and collected in jars. The volume of displaced water was measured accurately measuring

jar. This volume of water is equal to the volume of solids (Vs). Volume of solid (Vs) was subtracted from

the total volume of cube (V) (150mm X 150mm X150mm) to find the volume of voids (Vv) in the cube

specimen. Void ratio (e) was derived from the formula:-

Void Ratio , e= Volumeof voidsVolumeof solids

=VvVs

=V−VsVs

Porosity , n=Volume of voidsTotalVolume

=VvV

=V−VsV

The relationship between void ratio (e) and porosity (n) ids expressed as:-

n= e1+e

3.4.10 Permeability of Pervious ConcretePermeability of concrete generally refers to the rate at which water or other aggressive

substance (sulphates, chlorides ions, etc.) can penetrate concrete. It plays an important role in the

long-term durability of concrete. Lower the permeability higher the durability of concrete. But in

pervious concrete the permeability should be high for allowing infiltration and percolation of storm

water to underlying soil, reducing runoff volume, peak flow, pollutant loads and facilitating

groundwater recharge. Permeability of concrete primarily depends upon its porosity. There are different

methods for finding the permeability of concrete and they are:-

1. Constant Head Method

The basic concept of Constant Head Method is to make water flow through concrete

under constant pressure and measure the flow rate under Steady – State flow condition. The

specimens were placed in the test cells and the annular space was filled with some sealing

compound so that the flow occurred only in one direction i.e. from top to bottom.

Measurements were taken at the bottom surface after achieving the Steady-State flow

condition. Darcy’s law has been used to determine the co-efficient of permeability. The

equation used is

K s=QLAH

Where, Ks – Coefficient of saturated permeability (m/s)

Q – Volume of flow rate (m3/s)

A – Cross-sectional area (m2)

L – Specimen thickness in the direction of flow (m)

H – Head of water causing flow (m)

2. Falling Head Method

The falling head permeability test involves flow of water through a sample connected to a

standpipe which provides the water head and also allows measuring the volume of water passing through

the sample. Before starting the flow measurements, the sample is saturated and the standpipes are filled

with water to a given level. The test then starts by allowing water to flow through the sample until the

water in the standpipe reaches a given lower limit. The time required for the water in the standpipe to

drop from the upper to the lower level is recorded. Often, the standpipe is refilled and the test is repeated

for couple of times. The recorded time should be the same for each test within an allowable variation of

about 10%  (Head 1982) otherwise the test is failed. On the basis of the test results, the permeability of the

sample can be determined by Darcy’s law. The general expression for ‘k’ is

K s= aLA(t 1−t 0)

logeh0

h1

Where, Ks – Coefficient of saturated permeability (m/s)

A – Cross section area of sample (m2)

L – Height of the sample column (m)

a – Cross section area of the standpipe (m2)

(t1 – t0) – Recorded time for water column to flow through the sample (sec)

h0 – Upper water level in the standpipe measured using the same water head reference

h1 – Lower water level in the standpipe measured using the same water head

reference

Out of these two constant head method was adopted for the research. Apparatus was prepared

from the local market. Research experiments were performed at tubwell because high flow rate of water is

required to perform the experiment. After creating a constant head, the outlet water is collected in bucket

3 times for each specimen and time of flow was recorded with the help of stop watch.

Constant Head Apparatus