Effect of Shape and Size of Aggregate on the Properties of Pervious Concrete

By
A.K. Jain
Lecturer, Civil Engineering (Selection Grade), S.V. Polytechnic College, Bhopal M.P. 462-002, India

S.S. Goliya
Asst. Professor SATI (Degree) Vidisha M.P.464001, India

Dr. J.S. Chouhan
Professor and Head, Civil Engineering Deptt, SATI (Engineering College) Vidisha, M.P. 464-001, India

Abstract:
This paper presents the laboratory results of the study undertaken to determine the effect of shapes and size of aggregates on porosity, unit weight, strength and permeability of pervious concrete. Shape of aggregate is measured in terms of their angularity number. Angularity or absence of rounding of the particles of an aggregate is a property which is of importance because it affects the porosity, surface area in contact with each other in the matrix of ingredients and ease of handling of a mixture of aggregate and binder. It is a laboratory method intended for comparing the properties of different aggregates for mix design purposes. The result indicates that various properties of pervious concrete vary as a function of angularity number of aggregates used. It is found that for all sizes of course aggregates used in the study, aggregate with less angularity number produce mix with average compressive strength greater then the aggregate with higher angularity number. The study suggest that angularity number of aggregates may be considered as an important parameter in deciding the suitability of course aggregate to prepare pervious concrete mix in order to achieve better strength and permeability.

Keywords:
Angularity number; pervious concrete; compressive strength.


1. Introduction:
Pervious concrete is a specialty engineered concrete that allows water and air to pass through it. In literature, it has also been referred with various names such as no-fines concrete, enhanced porosity concrete, open graded, gap graded, porous concrete etc. It consists of Portland cement, coarse aggregate, little or no fine aggregate, admixtures, and water [1]. Combination of these ingredients when mixed, placed, compacted and cured properly, produce a hardened material that not only has sufficient strength and durability to bear the specified load and to resist environmental conditions but also have inter connected pores provide adequate permeability to the material which allow water to pass through easily.

As the urban areas are expanding, covering of natural surfaces with impervious materials is also increasing correspondingly in the form of roofs, pavements, parking lots etc. This situation causes many environmental problems including the problem of reduced ground water recharging, increase in quantity and pollution level of storm water etc. which triggers a chain effect encompassing the whole ecosystem of the watershed.

A substantial population on the globe depends on ground water to meet their needs and draw a substantially large quantity of water from under ground water bearing strata. Wide concern is being shown by technologist, development professionals, sociologist and economists about the sustainability of this major and inimitable source of water, considering the vast difference between the current increasing rates of withdrawal of water from aquifers and their reducing rate of recharging. Over exploitation of aquifers coupled with human interventions that interferes natural infiltration mechanism have resulted in to sinking of ground water table in almost all the urban or industrial settings on the globe. In many places, ground water reserves have been depleted to the extent that well yield have decreased, pumping cost have risen, water quality has deteriorated, aquatic ecosystem have been damaged and land has irreversibly subsided [2].

Increased paving of natural surfaces with impervious materials hamper its ability to infiltrate water to contribute to ground water reservoir, contrarily it convert the major quantity of rain water in to storm water which leaves the site carrying all the pollutants deposited on the paved surfaces with it. As the paved surfaces offers lesser ground obstructions to the flow of storm water, it leaves the site in higher rates. This increased quantity and deteriorated quality of stormwater, leads to downstream flooding, bank erosion, pollution of water bodies and an overall imbalance in the ecosystem of the watershed. Estimates of the impact that stormwater has on water resources in the United States indicate that up to 13% of impaired rivers, 18% of impaired lakes, and 32% of impaired estuaries are affected by stormwater runoff in urban or suburban areas (EPA, 2005). This has lead to an increased awareness in recent years, globally, toward need to recharge the ground water supplies, reducing the quantity of storm water generated from developed areas, reducing discharge of pollutants in water supplies and minimizing the effect of development on watersheds.

Pervious concrete pavement is one of the methods excepted to reduce the impact of development by allowing the rain water to percolate in the soil below, recharging the ground water aquifers, reducing the volume of direct water runoff from pavement and enhance the quality of storm water (Water Environment Research Foundation 2005). Pervious concrete is used to allow stormwater to infiltrate through the pavement and reduce or eliminate the need for additional control structures, such as retention ponds [3]. Currently pervious concrete pavement is increasingly being used in the United States for parking lots, pathways, low-volume roads, etc. for stormwater applications [4].

PCPC has been used for over 30 years in many countries, especially in the United States and Japan for its various environmental and functional benefits such as controlling storm water runoff, restoring groundwater supplies reducing water and soil pollution, improved skid resistance on roads, less noise generation due to tyre pavement interaction on pervious concrete road etc. [3] [4].

2. Literature Survey:
The National Ready Mix Concrete Association (2004) reported the mix design of ten projects where pervious concrete was used in the United States. Table- 1 summarizes the mix design used in these projects as well as that of suggested by Tennis et al. [3, 4]

Table 1 Typical mix design of existing Portland Cement Pervious Concrete

Ingredient	Quantity
	NRMCA, 2004	Tennis et al, 2004
Cement/ Cementitious Material (kg/m3)	178 – 356	270 to 415
Coarse aggregate (kg/m3)	1424 – 1602	1190 to 1480
Fine aggregate/ Fine: coarse aggregate ratio     (by mass)	0	0 to 1:1
Water/Cement ratio (by mass)	0.27 – 0.43	0.27-0.34
Aggregate/ Cement ratio (by mass)	-	4 to 4.5 : 1

Tennis reports that water to cementitious material ratio between 0.27 to 0.30 are used routinely with proper inclusion of chemical admixtures, and those as high as 0.34 and 0.4 have been used successfully [4]. Void contents of pervious concrete usually vary in the range of 15% to 25%. Because of its high void contents, compressive strength tends to be lower than those of standard concrete. NRMCA reports that pervious concrete can be designed to attain a compressive strength ranging from 2.8 to 28 MPa though strengths of 2.8 to 10 MPa are more common [5] whereas Tennis et al. reported that pervious concrete mixtures can develop compressive strengths in the range 3.5 MPa to 28 MPa, which is suitable for a wide range of applications [4]. For low-volume pavement design of pervious concrete, the NRMCA suggests using a 28-day compressive strength of 17 MPa (NRMCA 2004). However, 17 MPa is less than the compressive strength required for most conventional applications, typically 24.1-27.6 (Kosmatka et al. 2002, Schaefer VR et al 2006) the use of pervious concrete has been limited primarily to parking lots sidewalks, and low traffic density areas. [4].

The drainage rate of pervious concrete pavement vary with aggregate size and density of the mixture, but will generally fall into the range of 81 to 730 L/min/m2. [1] The correct consistency is usually obtained through a trial-and inspection process. Squeezing and releasing a handful of the mixed concrete should result in a mixture that neither crumbles nor becomes void-free, and no cement paste should flow away from the aggregate particles. The water to cement ratio is considered to be sufficient which ensures the mix with sufficient cement paste to coat the coarse particles with a shiny film, giving it a metallic gleam [1].

Wide experimentation has been conducted in past few decades by researchers to find out the effect of various fundamental parameters of pervious concrete including water-cementitious material ratio (W/CM) , Aggregate- Cement ratio(A/C), size of coarse aggregate etc on void content, unit weight, strength and permeability of pervious concrete [3-8], however the effect of shape of aggregate measured as Angularity Number of the aggregate on the above mentioned properties of pervious concrete has not been established.
Angularity or absence of rounding of the particles of an aggregate is a property which is of importance because it affects the arrangement of particles, void content, contact area between aggregates particles in the matrix of ingradients and ease of handling of a mixture of aggregate and binder, for example the workability of concrete or the stability of mixtures that rely on the interlocking of the particles. It is a laboratory method intended for comparing the properties of different aggregates for mix design purposes [IS: 2386 (Part I) - 1963]. It is believed that angularity number test will prove to be an important indicator to decide about the suitability of the aggregate to produce strong and durable pervious concrete.

Understanding of the effect of angularity number of course aggregate on void content, unit weight, strength and permeability of pervious concrete will provide a broad guideline in identification of suitability of course aggregates to produce pervious concrete not only of sufficient strength and durability but also having enough interconnected void ratio, thereby helping the material to perform the intended function. As often, local concrete producers best determine the mix proportions for locally available materials based on trial batching and experience, this information will also help to reduce number of trials to find out an optimum mix proportion of desired properties. The purpose of this study is, therefore, to study the preferred shape of aggregate to produce pervious concrete.

3. Research Objective and Scope
The objective of the present study is to evaluate the effect of angularity number of course aggregate on void content, unit weight, compressive strength and permeability of pervious concrete. The outcome of this research may assist and guide the professional for selection of appropriate aggregate type to be used in pervious concrete mix design.

In this study, three types and three sizes of single-sized course aggregates (12.5 mm, 10 mm and 6.3 mm) having different shape characteristics were used. Various relevant physical and mechanical properties of aggregate samples were determined and their effect on void content, unit weight, compressive strength and permeability properties of pervious concrete were evaluated.

The expected results of this research work shall be the relationship of angularity number of different types and single sizes of aggregates with void ratio, unit weight, compressive strength and permeability of pervious concrete at 28 days of age.

4. Experimental study
The testing plan was devised to determine the shape characteristics of the aggregate, flakiness index, Los Angel’s abrasion value, water absorption, specific gravity, unit weight, void content and angularity number of the collected aggregate sample. Details of material, mix proportion, sample preparation and test method used is as follows:

4.1. Materials
4.1.1 Cement: Portland pozzolana cement (Fly Ash based) obtained from local supplier, having fly ash content 25% and specific gravity 2.9 was used in the experiments. Properties of cement are given in Table 2.

Table 2: Properties of Cement used in Experiment.

S. No.	Particulars	Laboratory Test Values	Requirements of IS:1489-1991 (Part-1)
1.	Standard Consistency (%)	30
2.	Setting Time (minutes)
	a. Initial	155	30	Min
	b. Final	270	600	Max
3.	Compressive Strength (MPa)
	a. 168 +/- 2 hr. (7 days)	37.0	22	Min
	b. 672 +/- 4 hr. (28 days)	49.0	33	Min

4.1.2 Aggregates:
The coarse aggregate used in pervious concrete is typically single size rounded river gravel or a crushed stone. [Schafer et al]. Tennis et al. has reported that to manufacture pervious concrete, course aggregate is kept to a narrow gradation. Coarse aggregate having 9.5 mm top size has been used extensively for parking lot and pedestrian application. He also reported that typically higher strengths are achieved with rounded aggregates, although angular aggregates generally are suitable [Tennis et al].

On the basis of the above recommendations and other referred literature for this study, three different types of course aggregates having different shape characteristics were collected from two different local stone crushing plants. Based on their shape characteristics the aggregates were classified as flaky, angular and irregular as described in IS: 2386 (Part I)-1963, [IS: 2386 (Part I)-1963, 6-7]. The test samples collected were separate them into single size fractions using IS standard sieves. Details of the pair of sieves used, size identification of the aggregate retained between pair of sieves (square mesh) and their properties are given in Table 3 (a) and 3 (b).

S. No	Shape Characteristics of the Aggregate	Flakiness Index	Aggregate Type	Los Angels Abrasion Value (%)	Mean Water Absorption (%)	Specific Gravity
1	Material having small thickness relative to the other two dimensions	40%	F (Flaky)	22	0.81	2.76
2	Possessing well defined edges formed at the intersection of roughly planner faces	11%	A (Angular)	17	0.78	2.77
3	Partly shaped by attrition and having rounded edges	6 %	I (Irregular)	11	0.62	2.77

Table 3 (a). Properties of aggregate used in experimental study
Table 3 (b): Properties of aggregate used in experimental study

Aggregate Type (Sample)	Aggregate as retained between the pair of Sieves	Aggregate Identification	Compacted Unit Weight (kg/m3)	Voids (%)	Angularity Number	Average Angularity Number
F (Flaky)	16 mm and 12.5 mm	F-12.5	1454	47.32	13	13
	12.5 mm and 10 mm	F-10	1439	47.86	14
	10 mm and 6.3 mm	F-6.3	1463	46.99	13
A (Angular)	16 mm and 12.5 mm	A-12.5	1582	42.89	10	10
	12.5 mm and 10 mm	A-10	1569	43.36	10
	10 mm and 6.3 mm	A-6.3	1563	43.57	11
I (Irregular)	16 mm and 12.5 mm	I-12.5	1672	39.69	7	7
	12.5 mm and 10 mm	I-10	1663	39.96	7
	10 mm and 6.3 mm	I-6.3	1658	40.14	7

4.1.3 Water: Potable water used for preparation of mix and curing of concrete sample.
As the scope of the study is limited to find out the effect of angularity number of aggregate used in pervious concrete, chemical admixtures is not used in the study.

4.2 Mix proportions
Aggregate cement (A/C) ratio and water cementitious material (W/CM) ratio used in the study were decided on the basis of the various previous studies referred. Wanielista M. et al, (2006) concluded in a study that an increase in A/C ratio results in decrease in the compressive strength of pervious concrete but the mix with A/C ratio 6 and above provided least compressive strength [Wanielista M ]. Schaefer VR et al also reported that binder to aggregate ratio varied from 0.2 to 0.24, with a ratio of 0.21 found to provide the best particle coverage without excess cement paste [Schaefer]. On the basis of findings and conclusions drawn in these studies, experimental mix was prepared using A/C ratio equal to 4 and W/CM varying from 0.30 to 0.45 with increment of 0.03. Different mix were given a distinct identification number in which the first letter defines the type of aggregate like Flaky, Angular or Irregular (F/A/I) based on their surface characteristics, second figure indicates the size of the aggregate (12.5 mm, 10 mm, and 6.3 mm), third and fourth figure indicates Aggregate-Cement ratio and Water-Cement ratio respectively. Void content, unit weight, compressive strength, and permeability of the pervious concrete mix so prepared were determined. On the basis of the results obtained, effect of angularity number of aggregate on pervious concrete properties were evaluated.

Proportion of ingradients to prepare mix using different aggregate types is given in Table 4.

Table 4: Details of the Mix Proportion of Pervious Concrete

Mix ID	SG	Bulk Den of Agg (kg/m3)	Voids in Agg (%)	Wt of Agg (kg)	Wt. of Cement (kg)	Wt of Water (kg)
F- 12.5- 4.0- 0.30	2.76	1454	47.32	1454	364	109
F- 10- 4.0- 0.30	2.76	1439	47.86	1449	362	109
F- 6.3- 4.0- 0.30	2.76	1463	46.99	1463	366	110
F- 12.5- 4.0- 0.33	2.76	1454	47.32	1454	364	120
F- 10-4.0- 0.33	2.76	1439	47.86	1449	362	120
F- 6.3-4.5-0.33	2.76	1463	46.99	1463	366	121
F- 12.5- 4.0- 0.36	2.76	1454	47.32	1454	364	131
F- 10- 4.0- 0.36	2.76	1439	47.86	1449	362	130
F- 6.3- 4.0- 0.36	2.76	1463	46.99	1463	366	132
F-12.5- 4.0- 0.39	2.76	1454	47.32	1454	364	142
F-10- 4.0- 0.39	2.76	1439	47.86	1449	362	141
F- 6.3- 4.0- 0.39	2.76	1463	46.99	1463	366	143
F- 12.5- 4.0- 0.42	2.76	1454	47.32	1454	364	153
F- 10- 4.0- 0.42	2.76	1439	47.86	1449	362	152
F- 6.3- 4.0- 0.42	2.76	1463	46.99	1463	366	154
F- 12.5- 4.0- 0.45	2.76	1454	47.32	1454	364	164
F- 10- 4.0- 0.45	2.76	1439	47.86	1449	362	163
F- 6.3- 4.0- 0.45	2.76	1463	46.99	1463	366	165
A- 12.5- 4.0- 0.30	2.77	1582	42.89	1582	396	119
A- 10- 4.0- 0.30	2.77	1569	43.36	1569	392	118
A- 6.3- 4.0- 0.30	2.77	1563	43.57	1562	391	117
A- 12.5- 4.0- 0.33	2.77	1582	42.89	1582	396	131
A- 10-4.0- 0.33	2.77	1569	43.36	1569	392	129
A- 6.3- 4.5- 0.33	2.77	1563	43.57	1562	391	129
A- 12.5- 4.0- 0.36	2.77	1582	42.89	1582	396	142
A- 10- 4.0- 0.36	2.77	1569	43.36	1569	392	141
A- 6.3- 4.0- 0.36	2.77	1563	43.57	1562	391	141
A- 12.5- 4.0- 0.39	2.77	1582	42.89	1582	396	154
A- 10- 4.0- 0.39	2.77	1569	43.36	1569	392	153
A- 6.3- 4.0- 0.39	2.77	1563	43.57	1562	391	152
A- 12.5- 4.0- 0.42	2.77	1582	42.89	1582	396	166
A- 10- 4.0- 0.42	2.77	1569	43.36	1569	392	165
A- 6.3- 4.0- 0.42	2.77	1563	43.57	1562	391	164
A- 12.5- 4.0- 0.45	2.77	1582	42.89	1582	396	178
A- 10- 4.0- 0.45	2.77	1569	43.36	1569	392	177
A- 6.3- 4.0- 0.45	2.77	1563	43.57	1562	391	176
I- 12.5- 4.0- 0.30	2.77	1672	39.64	1672	418	125
I- 10- 4.0- 0.30	2.77	1663	39.96	1663	416	125
I- 6.3- 4.0- 0.30	2.77	1658	40.14	1636	409	123
I- 12.5- 4.0- 0.33	2.77	1672	39.64	1672	418	138
I- 10-4.0- 0.33	2.77	1663	39.96	1663	416	137
I- 6.3- 4.5- 0.33	2.77	1658	40.14	1658	409	137
I- 12.5- 4.0- 0.36	2.77	1672	39.64	1672	418	150
I- 10- 4.0- 0.36	2.77	1663	39.96	1663	416	150
I- 6.3- 4.0- 0.36	2.77	1658	40.14	1658	409	149
I- 12.5- 4.0- 0.39	2.77	1672	39.64	1672	418	163
I- 10- 4.0- 0.39	2.77	1663	39.96	1663	416	162
I- 6.3- 4.0- 0.39	2.77	1658	40.14	1658	409	162
I- 12.5- 4.0- 0.42	2.77	1672	39.64	1672	418	176
I- 10- 4.0- 0.42	2.77	1663	39.96	1663	416	175
I- 6.3- 4.0- 0.42	2.77	1658	40.14	1658	409	174
I- 12.5- 4.0- 0.45	2.77	1672	39.64	1672	418	188
I- 10- 4.0- 0.45	2.77	1663	39.96	1663	416	187
I- 6.3- 4.0- 0.45	2.77	1658	40.14	1658	409	187

4.3 Sample preparation:
Concrete were mixed in batches of a volume of approximately 25 liters, to prepare required number of cube and cylindrical specimen to perform the required tests.

A 140 liters tilting concrete mixer was used to mix the ingradients. Buttering of mixer was done each time before beginning the mixing of concrete by charging the mixer with cement and water in the proportion which is in the proposed mix.

To feed the ingradients in the mixer machine, first the saturated surface dry aggregates and required quantity of cement were measured. Then about half of the quantity of course aggregate were poured in to the mixer over which cement was placed and thereafter rest quantity of the aggregate was placed. The ingradients were mixed by pouring about 50 percent of total quantity of water required for the mix. Materials were mixed for one minute, then the rest quantity of water was added in to the drum. The concrete was further mixed for three minutes, and observed for the homogeneity of the mix before discharging it for casting of the samples.

Samples were casted by filling the mould in three layers, each of approximately 50 mm deep. Each layer was subjected to 35 strokes by the tamping bar conforming to IS: 10086-1982. After the top layer has been compacted, the surface of the concrete was finished level with the top of the mould, using a trowel, and covered with a glass or metal plate to prevent evaporation. The test specimens were kept covered with wet gunny bags in a place with approximately 90% relative humidity and at a temperature of 27 +- 2^oC for 24 +- ½ hours. After this duration the specimen were removed from the molds and marked properly for its identification, and submerged in clean fresh water. Samples were taken out of the water tank about one hour prior to the test.

Cylindrical specimen (dia100 mm and 150 mm height) were used to determine permeability of the concrete. These samples were casted in PVC pipes of 100 mm internal diameter using same method as were used for the compaction of cube mould.

4.4. Test methods
Flakiness index and angularity number of the aggregate sample were determined using the procedure as explained in IS: 2386 (Part I)- 1963, specific gravity, bulk density, Void contents and water absorption of the aggregate sample were determined using the procedure as explained in IS: 2386 (Part III)- 1963 and Los Angels Abrasion Value of the aggregate used in the study were determined using the procedure as explained in IS: 2386 (Part IV)- 1963. The void content of pervious concrete was determined by calculating the difference in weight between the air dried sample and the saturated under water sample, using the following equation (Park and Tia 2004, Schaefer et al. 2006, Delatte N. et al. 2007),

Vr(%) = [1-{(W₂-W₁)/ (pw*V)}]*100

Where:
Vr = total void ratio in percent; W₁ = weight under water in kg; W₂ = oven dry weight in kg; pw = density of water in kg/m³ and V = volume of sample in m³.

The unit weight of hardened samples was measured using oven dry weight. Compressive strength tests were performed according to IS: 512-1959 and the permeability of mixes was determined using a constant head permeameter devised for this purpose.

5. Test results and discussions
Results of the various experiments performed to evaluate the influence of the Shape of aggregate measured in terms of its angularity number on different pervious concrete properties is given in Table 5.

Table 5: Properties of Pervious concrete of different mix proportions

Mix ID	Unit Wt. (kg/m3)	Porosity (%)	Comp. St. MPa	Permeability mm/hr.	Remark
F- 12.5- 4.0- 0.30	1712	32.84	2.14	4539	VD, DSA
F- 10- 4.0- 0.30	1718	31.13	2.37	3975	VD, DSA
F- 6.3- 4.0- 0.30	1728	32.65	2.96	3800	VD, DSA
F- 12.5- 4.0- 0.33	1724	32.28	2.67	3595	DSA
F- 10-4.0- 0.33	1722	30.93	3.00	3276	VD, DSA
F- 6.3-4.0-0.33	1744	31.23	3.84	3208	VD, DSA
F- 12.5- 4.0- 0.36	1751	29.71	2.81	2892	MSA
F- 10- 4.0- 0.36	1757	29.01	3.24	2765	DSA
F- 6.3- 4.0- 0.36	1772	30.45	3.98	2664	VD, DSA
F-12.5- 4.0- 0.39	1794	28.13	3.31	2548	MSA
F-10- 4.0- 0.39	1808	27.31	3.49	2304	MSA
F- 6.3- 4.0- 0.39	1818	25.54	4.34	2162	DSA
F- 12.5- 4.0- 0.42	1822	25.93	3.70	1538	MSA
F- 10- 4.0- 0.42	1832	26.76	4.07	1235	MSA
F- 6.3- 4.0- 0.42	1844	24.66	5.43	1268	MSA
F- 12.5- 4.0- 0.45	1871	24.22	3.37	1356	MSA
F- 10- 4.0- 0.45	1877	23.07	4.10	1221	MSA
F- 6.3- 4.0- 0.45	1892	23.37	5.40	1067	MSA
A- 12.5- 4.0- 0.30	1897	25.23	3.77	2145	VD, DSA
A- 10- 4.0- 0.30	1928	24.06	4.42	1985	VD, DSA
A- 6.3- 4.0- 0.30	1948	25.05	5.50	1732	VD, DSA
A- 12.5- 4.0- 0.33	1921	24.27	4.52	1890	DSA
A- 10-4.0- 0.33	1947	23.53	5.29	1678	DSA
A- 6.3- 4.0- 0.33	1978	24.38	6.15	1436	VD, DSA
A- 12.5- 4.0- 0.36	1962	21.32	5.62	1679	MSA
A- 10- 4.0- 0.36	1975	20.08	6.52	1468	MSA
A- 6.3- 4.0- 0.36	2012	20.85	7.24	1289	DSA
A- 12.5- 4.0- 0.39	1991	18.21	6.55	1357	MSA
A- 10- 4.0- 0.39	2037	17.88	7.85	1157	MSA
A- 6.3- 4.0- 0.39	2042	17.51	9.62	976	MSA
A- 12.5- 4.0- 0.42	2021	17.38	6.73	978	PDD
A- 10- 4.0- 0.42	2047	16.11	7.71	786	MSA
A- 6.3- 4.0- 0.42	2062	16.15	9.42	732	MSA
A- 12.5- 4.0- 0.45	2053	14.77	5.77	194	PDD
A- 10- 4.0- 0.45	2067	14.22	6.73	118	PDD
A- 6.3- 4.0- 0.45	2099	13.17	7.95	97	MSA
I- 12.5- 4.0- 0.30	2075	16.78	4.10	1072	DSA
I- 10- 4.0- 0.30	2084	15.62	5.90	784	DSA
I- 6.3- 4.0- 0.30	2108	15.25	8.29	683	DSA
I- 12.5- 4.0- 0.33	2137	15.23	5.47	654	MSA
I- 10-4.0- 0.33	2115	15.04	7.41	378	MSA
I- 6.3- 4.0 – 0.33	2093	13.58	9.12	459	MSA
I- 12.5- 4.0- 0.36	2093	13.13	6.01	469	MSA
I- 10- 4.0- 0.36	2134	13.12	8.84	342	MSA
I- 6.3- 4.0- 0.36	2142	12.49	9.76	234	MSA
I- 12.5- 4.0- 0.39	2157	11.31	6.36	88	PDD
I- 10- 4.0- 0.39	2175	11.30	10.02	76	MSA
I- 6.3- 4.0- 0.39	2194	10.78	11.50	61	MSA
I- 12.5- 4.0- 0.42	2183	10.35	6.28	34	PDD
I- 10- 4.0- 0.42	2199	10.17	8.49	52	PDD
I- 6.3- 4.0- 0.42	2220	9.67	10.98	59	MSA
I- 12.5- 4.0- 0.45	2217	8.77	5.85	23	PDD
I- 10- 4.0- 0.45	2225	8.31	8.62	38	PDD
I- 6.3- 4.0- 0.45	2246	8.24	9.42	42	PDD

Remark*:
VD, DSA- Very dry mix with dull surface appearance. (Highly unsatisfactory mix)
DSA- Dry surface appearance (Unsatisfactory mix)
MSA- Metallic sheen appeared throughout the mix. (Satisfactory mix)
PDD- Paste drain down (Dripping of paste at the bottom of the cube leading to clogging of the pores)

5.1 Effect of Angularity Number (AN) on Void Contents:
The results of the void contents in the pervious concrete, prepared using aggregate with different angularity number and using different W/C ratio are shown in Table 6

Table 6: Relationship between angularity number of the aggregate and void contents of pervious concrete.

Relationship Between Angularity Number of Aggregates used and Void Contents in the Pervious Concrete Mix (A/C ratio 4)
AN	Void Contents
	W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate
	0.3			0.33			0.36			0.39			0.42			0.45
	12.5	10	6.3	12.5	10	6.3	12.5	10	6.3	12.5	10	6.3	12.5	10	6.3	12.5	10	6.3
13	32.84	31.13	32.65	32.28	30.93	31.23	29.71	29.01	30.45	28.13	27.31	25.54	25.93	26.76	24.66	24.22	23.07	23.37
10	25.23	24.06	25.05	24.27	23.53	24.38	21.32	20.08	20.85	18.21	17.88	17.51	17.38	16.11	16.15	14.77	14.22	13.17
7	16.78	15.62	15.25	15.23	15.04	13.58	13.13	13.12	12.49	11.31	11.30	10.78	10.35	10.17	9.67	8.77	8.31	8.24

As it is known that the void contents of a mix is a function of many factors, including shape and size of aggregate used in the mix. It was found that the average void ratios tend to increase as the angularity number of aggregate used in the mix increases for all sizes of aggregate and W/CM ratio. Figure 1 gives the graphical representation of the variation of void content with respect to the angularity number of the aggregate used in the mix. For all series, there exists a linear relationship between angularity number of the aggregate and void contents. The void contents increase as the angularity number increases.

Figure 1: Relationship between angularity number of the aggregate used and Void contents of pervious concrete for different size of aggregate and W/CM ratio..

5.2 Effect of Angularity number on Unit Weight.
It has been observed that for all types, sizes and W/CM ratio, there exists an inverse linear relationship between angularity number and unit weight of pervious concrete. The unit weight for all mixes prepared in the experiment decreases linearly as a function of angularity number. Table 7 and Figure 2 shows the observed relationship. It clearly demonstrates that mixes with the lowest angularity number produce pervious concrete mix with highest unit weight.

Table 7: Relationship between Angularity Number and Unit Weight of Pervious Concrete.

Relationship Between Angularity Number of Aggregates And Unit Weight of the Pervious Concrete Mix (A/C ratio 4)
AN	Unit Weight (kg/m3)
	W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate
	0.3			0.33			0.36			0.39			0.42			0.45
	12.5	10	6.3	12.5	10	6.3	12.5	10	6.3	12.5	10	6.3	12.5	10	6.3	12.5	10	6.3
13	1712	1718	1728	1724	1722	1744	1751	1757	1772	1794	1808	1818	1822	1832	1844	1871	1892	1892
10	1897	1928	1948	1921	1947	1978	1962	1975	2012	1991	2037	2042	2021	2047	2062	2053	2067	2099
7	2075	2084	2108	2137	2115	2093	2093	2134	2142	2157	2175	2194	2183	2199	2220	2217	2225	2246

Figure 2: Relationship between angularity number of the aggregate used and unit weight of pervious concrete for different sizes of aggregates and W/CM ratio.

5.3 Effect of Angularity Number on Compressive Strength of Pervious Concrete.
Compressive strength of pervious concrete is generally related to strength of aggregate, strength of paste and void contents. For a given W/C ratio, pervious concrete with angular aggregate have produce higher strength and that of with irregular aggregate have produced maximum strength among the three aggregate type. Smaller strength demonstrated by flaky aggregates may be explained as under the load, in case of more flaky or more angular aggregate particles, the presence of sharp edged and corners in aggregates produces concentration of stress and get crushed at comparatively lower compressive load. Table 8 presents the experimental values of compression strength of the pervious concrete mix proportion used for various types/ shape of aggregates after an age of 28 days. Figure 3 presents a graphical presentation of the values. It is well demonstrated from the results obtained that the shape of aggregate influences the compressive strength of pervious concrete remarkably. For all sizes of aggregate and W/CM ratio, there exists an inverse relationship between angularity number and compressive strength of pervious concrete as the compressive strength decreases with increase in angularity number. Also for aggregate with angularity number 13, all sizes of aggregates demonstrated maximum strength at W/CM ratio of 0.42 and 0.45, whereas for aggregate with angularity number 10, all sizes of aggregates demonstrated maximum strength at W/CM ratio of 0.39 and 0.42, and for aggregate with angularity number equal to 7, all sizes of aggregates demonstrated maximum strength at W/CM ratio 0.39.

Table 8: Relationship between Angularity Number and Compressive Strength of Pervious Concrete.

Relationship Between Angularity Number of Aggregates And Compressive Strength of the Pervious Concrete Mix (A/C ratio 4)
AN	Compressive Strength (MPa)
	W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate
	0.3			0.33			0.36			0.39			0.42			0.45
	12.5	10	6.3	12.5	10	6.3	12.5	10	6.3	12.5	10	6.3	12.5	10	6.3	12.5	10	6.3
13	2.14	2.37	2.96	2.67	3.00	3.84	2.81	3.24	3.98	3.31	3.49	4.34	3.70	4.07	5.43	3.37	4.10	5.40
10	3.77	4.42	5.50	4.52	5.29	6.15	5.62	6.52	7.24	6.55	7.85	9.62	6.73	7.71	9.42	5.77	6.73	7.95
7	4.10	5.90	8.29	5.47	7.41	9.12	6.01	8.84	9.76	6.36	10.02	11.50	6.28	8.49	10.98	5.85	8.62	9.42

Figure 3: Relationship between angularity number of the aggregate used and compressive strength of pervious concrete for different sizes of aggregates and W/CM ratio.

5.4 Effect of Angularity Number on Permeability of Pervious Concrete.
Table 9 and Figure 4 demonstrates the results of the experiments showing the variation in the permeability of pervious concrete as a function of the shape of the aggregates measured in terms of their angularity number. Few of the mixes, in which paste drain down effect was observed demonstrated proportionately less permeability because of accumulation of paste at the bottom of the sample casted. It is clearly demonstrated through the results that the effect of paste draw down is observed at different W/CM ratio for different shape and size of aggregates i.e. for flaky mix no draw down effect was observed in all the mixes; for angular aggregates, the effect was observed in mix A- 12.5- 4.0- 0.42 , A- 12.5- 4.0- 0.45, and A- 10- 4.0- 0.45 i.e. for 12.5 mm angular aggregate at W/CM ratio of 0.42 and 0.45 and for 10 mm angular aggregate at W/CM ratio of 0.45. Similarly for irregular aggregate, the effect is observed in mix I- 12.5- 4.0- 0.39, I- 12.5- 4.0- 0.42, I- 10- 4.0- 0.42, I- 12.5- 4.0- 0.45, I- 10- 4.0- 0.45, I- 6.3- 4.0- 0.45.
To avoid paste draw down effect, W/CM ratio shall be decided giving due consideration to shape and size of the aggregates. The permeability for all the other mixes is quite more than any precipitation rate observed. Reducing permeability rate has been observed for angular and irregular aggregate respectively as compared with flaky aggregate. Also for smaller size of aggregate the rate of permeability recorded is less.

Table 9: Relationship between angularity number of the aggregate and permeability of pervious concrete.

Relationship Between Angularity Number of Aggregates And permeability of the Pervious Concrete Mix (A/C ratio 4)
AN	Permeability (mm/hr)
	W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate			W/CM ratio & Size of Aggregate
	0.3			0.33			0.36			0.39			0.42			0.45
	12.5	10	6.3	12.5	10	6.3	12.5	10	6.3	12.5	10	6.3	12.5	10	6.3	12.5	10	6.3
13	9078	7950	7600	7190	6552	6416	5784	5530	5328	5096	4608	4324	3076	2470	2536	2712	2442	2134
10	4290	3970	3464	3780	3356	2872	3358	2936	2578	2714	2314	1952	1956	1572	1464	388	236	194
7	2144	1568	1366	1308	756	918	938	684	468	176	152	122	68	104	118	46	76	84

Figure 4: Relationship between angularity number of the aggregate and permeability of pervious concrete for different aggregate sizes and W/CM ratio.

6. Conclusion
For the pervious concrete pavement, to function as an engineered surface as a parking lot and at the same time allow all the rain water to pass through it in to the soil below, its porosity and strength both assume equal importance. As known from the literature, a wide variation in the strength of pervious concrete achieved in the field (2.8 to 28 MPa) has been observed. In order to make this material and technology exceptive, predictive and more certain, an understanding about the properties of aggregates that affect the strength and other characteristics of pervious concrete will be helpful in selection of ingredients and their proportion, so as to reduce the variation in the performance of material.

Angularity number of aggregate is a numerical index to measure the shape of aggregate. In India, presently there is no regulation in force to ensure that the aggregate manufactured by stone crushing industry shall have to comply with certain parameters. This leads to wide variation in the type and size of aggregate available at various crushing units and at a certain crushing unit at different time. This study reveals that shape and size of aggregate have demonstrated distinguishable impact on the pervious concrete properties. Flaky aggregate produce mix having more voids, less unit weight and compressive strength whereas angular and irregular aggregates produced pervious concrete with lesser voids, more unit weight and compressive strength respectively. For all the shapes of aggregates smaller size of aggregates produced concrete with more unit weight. Strength of pervious concrete increase with increase in W/CM ratio up to a certain value which is different for different shape and size of aggregate, thereafter it reduces with increase in W/CM ratio as in the case with regular concrete. As expected, results demonstrated the inverse relationship between void contents and compressive strength for all kind of mixes.

When load is applied on pervious concrete it transfers through the contact points of the aggregate particles and the layer of cement paste around these contact points. In the case of flaky or angular aggregate these contact points are in the form of sharp corners and edges, which tend to crush at lower load than that of in the case of the rounded aggregate. This seems to be a reason of smaller compressive strength of the mixes produced using flaky and angular aggregates in comparison to that of irregular aggregates.

Permeability of all the mixes is found to be in direct proportion to the void contents of the pervious concrete. In the study, mix A-12.5-4.0-0.42, A-12.5-4.0-0.45, A-10-4.0-0.45, I-12.5-4-0.39, I-12.5-4.0-0.42, I- 10- 4.0- 0.42, I- 12.5- 4.0- 0.45, I- 10- 4.0- 0.45 and I- 6.3- 4.0- 0.45 found to be suffered with drain down effect of cement paste resulted in to the reduced permeability of the mix. This suggest that Proper attention to optimize the W/CM ratio on case to case basis is very important to ensure that the pervious concrete will function its intended function of allowing water through it during service.

Presently the choice of aggregate mostly depends on its availability, although for a pervious concrete project, it is recommended to use the aggregate of smallest possible angularity number to ensure better compressive strength without compromising with any of the other properties.

References:
1. American Concrete Institute. 2006. “Pervious Concrete”, ACI Manual of Concrete Practice, 522R-06 Committee, Farmington Hills, MI.
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13. Jain A.K., Chouhan J.S., “Pervious concrete pavement: meeting environmental challenges”, Proceedings of the international conference on concrete construction, Exxcellance in Concrete Construction through Innovations, Kingston University, London UK, 9-10 September 2008, Page 553-558.
14. Jain A.K., Chouhan J.S., Dongre Ashish, “Pervious Concrete: An Environmental Friendly Material For Sustainable Development”, Proceeding of the International Seminar, Sustainable Concrete Construction Organised By India Chapter of American Concrete Institute, 8-10 February, 2008 Ratnagiri, Maharastra, India,. Page 209-213.

We at engineeringcivil.com are thankful to Sir A.K. Jain for submitting his research paper on “Effect of Shape and Size of Aggregate on the Properties of Pervious Concrete.” This will help civil engineers in understanding how the Shape and Size of Aggregate effects the Properties of Pervious Concrete.