Durability and mechanical properties of Portland cement concrete that utilizes crumb rubber as an alternative fine aggregat
Master of Science
DisciplineEngineering : Civil
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This research project investigated in an intensive experimental program the influence of using crumb rubber in the mechanical properties and durability of Portland cement concrete mixtures. Crumb rubber is produced from waste tires which pose significant problems in the waste management sector. The incorporation of crumb rubber in some concrete infrastructure will help reduce the number of tires stockpiled annually. Two rounds of batching and testing were undergone. One round occurred over the summer of 2017 and the other in the spring of 2018. The water cement ratio used in all mixes containing crumb rubber was 0.45. One mix with a water cement ratio of 0.4 was also prepared to give comparative values as to what would be obtained in a pavement structure designed meeting MTO criteria. Crumb rubber replaced a percent volume of the fine aggregate. Batches with crumb rubber substitution in amounts of 0 % to 25 %, in 5 % increments were prepared. Each mix was tested for 28-day compressive strength, flexural strength, splitting tensile strength, bulk resistivity, surface resistivity, rapid chloride penetration and freeze-thaw testing (ASTMC39, ASTMC78, ASTMC496, ASTMC1202, ASTMC666, respectively). The 28-day compressive strength, flexural strength and splitting tensile strength were all observed to decrease with the increase in crumb rubber. It was found that a 25 MPa 28 day compressive strengths are possible with crumb rubber replacing as much as 15% of the fine aggregate. The corresponding modulus of rupture of the mixture was 5.2 MPa compared to 5.9 MPa in a similar concrete mixture but without crumb rubber. The splitting tensile strength for the mixture containing 15 % of the fine aggregate crumb rubber was 2.9 MPa which is 90 % of the splitting tensile strength of a similar concrete mixture but with no rubber. Bulk resistivity, and surface resistivity as a function of the rubber content and the effect of the freeze freeze-thaw durability all improved, however the improvement was not statistically significant. The bulk resistivity was found to be 6.0 kΩcm for the mixture with 15 % of the fine aggregate crumb rubber and 5.9 kΩcm for the mixture containing no crumb rubber. Similarly, for surface resistivity the values were 17.4 kΩcm and 17.1 kΩcm for the 15 % and 0 % crumb rubber contents, respectively. The rapid chloride penetration values did improve, but again not significantly. In fact, the classification according to ASTM C1202 did not change. All samples were of moderate penetrability. For every 5 % increase in rubber as a portion of fine aggregate, it was found that the plastic air content increased 0.5 % above the measured mechanically entrapped air. Durability factors were not able to be calculated from freeze-thaw tests due to low fundamental frequency readings before any cycles. However, a plot of the relative dynamic moduli shows that the introduction of crumb rubber did significantly improve the durability of the concrete mixture. After 300 cycles the relative dynamic moduli of the mix with a 0.4 water cement ratio and no crumb rubber was 483, whereas a mix with a 0.45 water cement ratio and 15 % crumb rubber had a relative dynamic modulus of 773.