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Strength And Durability Performance Of Pervious Concrete

Posted on:2019-10-11Degree:MasterType:Thesis
Country:ChinaCandidate:Hassan BilalFull Text:PDF
GTID:2381330590974328Subject:Civil engineering
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Pervious concrete is an environmental friendly porous material developed on the basis of ordinary concrete technology.It typically contains Portland cement,coarse aggregate,various admixtures,water and little or no fine sand.Pervious concrete has lower strength associated with large porosity of interconnected network of voids intentionally formed in the structural system to infiltrate storm water runoff,recharge the ground water aquifer and significantly reduce the negative consequences of increase runoff during the storm event by minimizing erosion and sedimentation.The pores system or interconnected voids are advantageous for mitigating the negative environmental concerns pose by impervious surfaces in urban areas however,due to the limited cement paste coat encapsulating the aggregate particles in pervious concrete the strength of pervious concrete is meager with high infiltration capability.The lower strength associated with high porosity limited the application of pervious concrete to low volume traffic,parking lots,sidewalk,path way and the vulnerability to freeze thaw resistance is another perennial concern for pervious concrete in cold climate therefore,this experimental investigation was performed to understand the resistance of pervious concrete subjected to rapid freeze thaw cycling and frost damage mechanisms of pervious concrete under harsh wet saturated condition.This study uses silica fume,metakaolin,SBR latex polymer emulsion and sand in different proportion in the pervious concrete specimens.The optimization of mix design and mix proportion of raw materials were carried out to balance the strength and water permeability of pervious concrete.The freeze-thaw cycle performance of pervious concrete was evaluated based on mass loss criteria and visual inspection during test.The influence of various admixtures on the freeze-thaw cycle performance of pervious concrete were observed and the frost damage mechanism was discussed.The results of freeze-thaw cycle indicate that different admixtures have distinctive effects on the frost damage resistance of pervious concrete.The addition of fine sand 5% by weight of coarse aggregate and proper compaction had positive influence on improving the resistance of pervious concrete to rapid freeze-thaw cycling.The SBR latex had highest mass loss and poor resistance to freeze-thaw cycling due to high volume expansion and water uptake.The hydraulic pressure and critical degree of saturation developed in the high porous structure of SBR latex modified pervious concrete induced cracks which further widen with the increase in freeze-thaw cycling.The increased in dosage rate of admixtures from 5% to 10% by partial replacement of silica fume,metakaolin or both with cement content had further enhanced the resistance to frost damage in saturated condition although the pervious concrete had high voids associated with high porosity and high hydraulic pressure developed with the continual increase in freeze-thaw cycling.The control pervious concrete included only 5% fine sand had minimum mass loss and surface deterioration compared to modified pervious concrete produced with 5% partial replacement of cement with silica fume,metakaolin or both into the pervious concrete however the increased in cementitious materials from 5% to 10% reduced the mass loss and improved the resistance to rapid freeze-thaw cycling.The optimum dosage of 10% admixtures addition in pervious concretes was found to have significantly improve the freeze-thaw performance in saturated condition.The results show that calcium leaching in 6M ammonium nitrate solution coupled with freeze-thaw cycling produce more severe surface deterioration and internal damages in samples compared to individual damage mechanism of freeze-thaw cycling and calcium leaching.The performance of modified pervious concrete with silica fume(SF),metakaolin(MK)and binary combination of both(MK-SF)have more resistance to coupled action of leaching and freeze-thaw cycling compared to control mixture(S-5%)and polymer modified mixture(L).The SBR latex had very poor resistance in 6M ammonium nitrate solution and the chemical reaction between SBR latex and NH4NO3 caused the reduction in mass of SBR latex itself which had severely increase the mass loss of SBR latex modified cement paste and polymer modified pervious concrete.The leaching of calcium ion from the cement hydrates with the leaching duration increased and had significant influence on the mass loss and strength of concrete.The addition of silica fume and binary mixes contained both silica fume and metakaolin had best resistance in terms of calcium ion leaching from the cement paste and pervious concrete,however,metakaolin addition in mixes had lowest calcium ion leaching at early age but the leaching rate increased with the prolong leaching duration.The p H of aggressive leachate solution in initial stage of leaching test was about 6 and then rapidly increased above 9,however,the p H of leachate gradually evolved with leaching duration and tend to stabilized at prolong leaching duration.The p H values were within the range from 7.5 to 8.5 for all pervious concrete samples immersed in the aggressive solution except silica fume modified pervious concrete which had lower p H value due o least dissolution of calcium hydroxide and release of hydroxide anion into the aggressive solution.
Keywords/Search Tags:Performance
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