Porosity/ laboratory equipment indicating error between different operators

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).

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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).

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