دانلود رایگان مقاله انگلیسی ارزیابی تاثیر خورده لاستیک و نانو سیلیکا در ساختار خاکستر بادی بتن غلطکی پیاده رو - الزویر 2018

Abstract

The major problems related to roller compacted concrete (RCC) pavement are high rigidity, lower tensile strength which causes a tendency of cracking due to thermal or plastic shrinkage, flexural and fatigue loads. Furthermore, RCC pavement does not support the use of dowel bars or reinforcement due to the way it is placed and compacted, these also aided in cracking and consequently increased maintenance cost. To address these issues, high volume fly ash (HVFA) RCC pavement was developed by partially replacing 50% cement by volume with fly ash. Crumb rubber was used as a partial replacement to fine aggregate in HVFA RCC pavement at 0%, 10%, 20%, and 30% replacement by volume. Nano silica was added at 0%, 1%, 2% and 3% by weight of cementitious materials to improve early strength development in HVFA RCC pavement and mitigate the loss of strength due to the incorporation of crumb rubber. The nondestructive technique using the rebound hammer test (RHT) and ultrasonic pulse velocity (UPV) were used to evaluate the effect of crumb rubber and nano silica on the performance of HVFA RCC pavement. The results showed that the use of HVFA as cement replacement decreases both the unit weight, compressive strength, rebound number (RN). Furthermore, the unit weight, compressive strength, RN, UPV and dynamic modulus of elasticity of HVFA RCC pavement all decreases with increase in crumb rubber content and increases with the addition of nano-silica. Combined UPV-RN (SonReb) models for predicting the 28 days strength of HVFA RCC pavement based on combining UPV and RN were developed using multivariable regression (double power, bilinear, and double exponential models). The exponential combined SonReb model is the most suitable for predicting the compressive strength of HVFA RCC pavement using UPV and RN as the independent variable with better predicting ability, higher correlation compared to the single variable models.

4. Conclusions

The following conclusions were drawn based on the experimental work carried out and results analysis.

 The use of high volume fly ash (HVFA) as a partial replacement to cement in RCC pavement results to decreased unit weight, compressive strength, surface hardness (RN), UPV and dynamic modulus of elasticity.

 The incorporation of crumb rubber as a partial replacement to fine aggregate in HVFA RCC pavement leads to decrease in unit weight, compressive strength, and surface hardness (RN), UPV and dynamic modulus of elasticity.

 Nano silica increases the unit weight, compressive strength, surface hardness (RN), UPV, and dynamic modulus of elasticity of HVFA RCC pavement.

 Nano silica was successful in improving the early strength development in HVFA RCC pavement by igniting pozzolanic reactivity of fly ash at an early age.

 Nano silica was successful in mitigating the loss of compressive strength in HVFA RCC pavement when 10% crumb rubber was incorporated as a partial replacement to fine aggregate. For higher crumb rubber contents, nano silica partially mitigated the loss of compressive strength.

 A high degree of correlation exists between compressive strength – UPV, compressive strength – RN, and compressive strength – dynamic modulus of elasticity of HVFA RCC pavement.

 The exponential combined SonReb model is the most suitable for predicting the compressive strength of HVFA RCC pavement using UPV and RN as the independent variable.

 The combined SonReb model (multi-variable model) has the better predicting ability, higher correlation compared to the single variable models.