Porosity/ laboratory equipment indicating error between different operators

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Last updated: June 14, 2019

Porosity/ Pore sizes          A number of key properties in perviousconcrete, including permeability and Compressive strength, have been directlyrelated to the porosity of the material. Therefore, it is very important toobtain the porosity. In pervious concrete the total porosity/void content canbe determined as per ASTM C1688. Porosity can also be measured on concretespecimens including cores and cast cylinders by using the method developed byMontes et al.

(55) which was the basis for ASTM C1754 (113). And this method is widely reportedby 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 Effectiveporosity. Zhong and wille (12), in their calculation used the weight differencebetween an oven dried sample and a saturated sample to calculate effectiveporosity. It was also reported that higher proportion of coarse fractionresulted in a higher porosity (4).This is because the introduced coarserparticle 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 perviousconcrete mixtures with the increase in the compressive energy absorbed. Kim& lee (2010) Total void ratio of specimen are higher when smaller sizeaggregates are used.Theporosity of pervious concrete is an important variable needed for pavementsystem design and for material comparisons. In A study for measuring theporosity of field-obtained cores using the Archimedes principle and standardmaterials laboratory equipment indicating error between different operators atdifferent testing facilities to be around 2.2 % (55).

The porosity is an importantparameter and mainly depends on field placement techniques so it was alsorecommended to calculate the porosity of field-placed specimens based on the aggregatesize, core size and porosity (135). Alsoreported 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 bythe addition of super plasticizer and a thickening agent for high performancepervious concrete.Itis assumed that porosity remained constant along the depth but there existsvertical porosity distribution in pervious concrete (46,158). Their experimentalinvestigation reported that the porosity increases significantly from top tobottom being lowest porosities in the top quarter, average porosities in thecenter half, and the higher porosities near the bottom. Various stereologicaland morphological techniques were used to determine the distribution of poresin pervious concrete.

25. Lian et al. (91) proposed mathematical modelthat provide relation between porosity and compressive strength. Zhong andwille (13) reported the pore size distribution extracted from linear pathfunction that agrees well with image analysis.{Themodulus of elasticity influences response of any material under load, andporosity influences the hydraulic properties of pervious concrete.  In a research study, the relationship betweenporosity and modulus of elasticity of pervious concrete was also reported as ithas not been studied well yet (135). Theobjective of the study (138)is to define relationships between formulation parameters (like aggregate sizesand paste quantities) and final properties of pervious concrete (permeability,mechanical resistance, and porosity) through 3D images obtained bymicro-tomography, exploited mathematical morphology tools, such as two-pointcorrelation functions to access specific surface area, porosity value andgranulometric distribution of porosity.

The permeability of pervious concreteis finally estimated by solving the Stokes equation on the 3D pore networknumerically with finite elements. Permeability values obtained from 2D imagesand 3D acquisitions with water permeability measured in laboratory are thencompared.Reductionin porosity (or increase in bulk solid volume fraction) of the perviousconcrete mixtures were found to result in an increase in the compressive energyabsorbed by comp active efforts. The increasing degree of heterogeneity withincreasing aggregate sizes is obvious from this figure no.4. Since the mixtureshave similar porosities irrespective of the nominal maximum aggregate sizesused, 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) andcombination large and small pores in (9.

5mm) (56).Toproduce large size pores in the material, large size aggregate are recommended,it may reduce the chance of pore clogging. Also substituting smaller sizedaggregates with an increasing percentage of larger-sized ones increases thepore size.

A higher proportion of coarse fraction in mixtures results in ahigher value of overall porosity and A higher quantity of small aggregatefractions (4–8 mm) influenced the higher density of concrete mixtures andhigher flexural strength (4).Lian & zhuge (91) Developed mathematical model to correlate compressive strength and porosity andstudied through empirical and theoretical derivations. And reported that modelbetter agreement with experimental data and predict compressive strength basedon porosity. (H. Li et al. 2014 and Syrrakou et al. 2013), Delvedinto Evaporation rate studies, a simple test method of evaporation rate wasdeveloped.

Evaporation rate were measured for six permeable pavement materialsand factors affecting evaporation rate were explored. Methods to enhanceevaporation rate were proposed, theoretical studies are recommended to evaluateand optimally design the evaporative cooling effect of pavement materials withadequate permeability. The experimental work indicates that evaporation is anonlinear function of the amount of water present in the system.

The evaporation rates belong to the same order of magnitude (10?2mm/h).

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