Porosity/ Pore sizes

A number of key properties in pervious

concrete, including permeability and Compressive strength, have been directly

related to the porosity of the material. Therefore, it is very important to

obtain the porosity. In pervious concrete the total porosity/void content can

be determined as per ASTM C1688. Porosity can also be measured on concrete

specimens including cores and cast cylinders by using the method developed by

Montes et al. (55) which was the basis for ASTM C1754 (113). And this method is widely reported

by many researchers (9, 11, 18, 30, 65, 88, 157). While many researchers (46, 57, 64, 88)

also have used the method described in ASTM D7063 to calculate the Effective

porosity. Zhong and wille (12), in their calculation used the weight difference

between an oven dried sample and a saturated sample to calculate effective

porosity. It was also reported that higher proportion of coarse fraction

resulted in a higher porosity (4).This is because the introduced coarser

particle may not be able to fit in the void left by the removed finer particle

(Neithalath 2004, Neithalath et al. 2003).

O.

Deo & N. Neithalath. (36) Reported a reduction in porosity of the pervious

concrete mixtures with the increase in the compressive energy absorbed. Kim

& lee (2010) Total void ratio of specimen are higher when smaller size

aggregates are used.

The

porosity of pervious concrete is an important variable needed for pavement

system design and for material comparisons. In A study for measuring the

porosity of field-obtained cores using the Archimedes principle and standard

materials laboratory equipment indicating error between different operators at

different testing facilities to be around 2.2 % (55).The porosity is an important

parameter and mainly depends on field placement techniques so it was also

recommended to calculate the porosity of field-placed specimens based on the aggregate

size, core size and porosity (135). Also

reported in a study by that porosity is greatly affected by Recycle aggregate.

However,

Bhutta et al. (40) in their study also mentioned that the porosity is affected by

the addition of super plasticizer and a thickening agent for high performance

pervious concrete.

It

is assumed that porosity remained constant along the depth but there exists

vertical porosity distribution in pervious concrete (46,158). Their experimental

investigation reported that the porosity increases significantly from top to

bottom being lowest porosities in the top quarter, average porosities in the

center half, and the higher porosities near the bottom. Various stereological

and morphological techniques were used to determine the distribution of pores

in pervious concrete. 25. Lian et al. (91) proposed mathematical model

that provide relation between porosity and compressive strength. Zhong and

wille (13) reported the pore size distribution extracted from linear path

function that agrees well with image analysis.{The

modulus of elasticity influences response of any material under load, and

porosity influences the hydraulic properties of pervious concrete. In a research study, the relationship between

porosity and modulus of elasticity of pervious concrete was also reported as it

has not been studied well yet (135). The

objective of the study (138)

is to define relationships between formulation parameters (like aggregate sizes

and paste quantities) and final properties of pervious concrete (permeability,

mechanical resistance, and porosity) through 3D images obtained by

micro-tomography, exploited mathematical morphology tools, such as two-point

correlation functions to access specific surface area, porosity value and

granulometric distribution of porosity. The permeability of pervious concrete

is finally estimated by solving the Stokes equation on the 3D pore network

numerically with finite elements. Permeability values obtained from 2D images

and 3D acquisitions with water permeability measured in laboratory are then

compared.Reduction

in porosity (or increase in bulk solid volume fraction) of the pervious

concrete mixtures were found to result in an increase in the compressive energy

absorbed by comp active efforts. The increasing degree of heterogeneity with

increasing aggregate sizes is obvious from this figure no.4. Since the mixtures

have similar porosities irrespective of the nominal maximum aggregate sizes

used, the pore sizes will be larger in the mixtures with larger aggregate sizes

(12.5mm), and large number of small pores in small size aggregates (4.75mm) and

combination large and small pores in (9.5mm) (56).To

produce large size pores in the material, large size aggregate are recommended,

it may reduce the chance of pore clogging. Also substituting smaller sized

aggregates with an increasing percentage of larger-sized ones increases the

pore size. A higher proportion of coarse fraction in mixtures results in a

higher value of overall porosity and A higher quantity of small aggregate

fractions (4–8 mm) influenced the higher density of concrete mixtures and

higher flexural strength (4).

Lian & zhuge (91) Developed mathematical model to correlate compressive strength and porosity and

studied through empirical and theoretical derivations. And reported that model

better agreement with experimental data and predict compressive strength based

on porosity.

(H. Li et al. 2014 and Syrrakou et al. 2013), Delved

into Evaporation rate studies, a simple test method of evaporation rate was

developed. Evaporation rate were measured for six permeable pavement materials

and factors affecting evaporation rate were explored. Methods to enhance

evaporation rate were proposed, theoretical studies are recommended to evaluate

and optimally design the evaporative cooling effect of pavement materials with

adequate permeability. The experimental work indicates that evaporation is a

nonlinear function of the amount of water present in the system. The evaporation rates belong to the same order of magnitude (10?2

mm/h).