Key Engineering Materials Vol. 902

Abstract: Rutting, fatigue cracking and low temperature cracking are the most important distresses in asphalt pavements as a result of changes in rheological properties of asphalt binder. Many types of modifiers were used to enhance asphalt behavior at both low and high temperatures. In this study, carbon nanotubes (CNT) were used as one of many nanomaterials that take a large attention in the latest research related to asphalt modification against different types of distresses. Effect of CNT on rheological properties of asphalt binder was investigated by testing unmodified and CNT modified asphalt binders using two of Superpave devices: Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR). Penetration, softening point, flash point and rotational viscosity (RV) tests were carried out as well. CNT was added in 0.1%, 0.5% and 1% by weight of asphalt binder. It was found that adding CNT in 0.5% and 1% increase stiffness of asphalt and consequently asphalt pavement rutting resistance. On the other hand, this increase in stiffness affected pavement behavior adversely which is not desirable for fatigue and low temperature cracking. However, Superpave specifications were still satisfied and asphalt binder’s relaxation properties were improved upon CNT modification. It was eventually found that 0.5% of CNT is the optimum percentage for the best performance.

Abstract: Ordinary Portland cement (OPC) is one of the most widely used construction materials in civil engineering infrastructure construction but it is susceptible to sulfate attack. One of the ways to improve the sulfate resistance of an OPC mortar/concrete is to replace a certain amount of OPC with different pozzolanic materials such as ground granulated blast furnace slag (GGBFS) and metakaolin. The use of pozzolanic materials to mortar/concrete not only enhances durability but also reduces carbon dioxide (CO₂) emission due to the less usage of OPC at the initial construction state. As considering these aspects, limestone calcined clay cement (LC3) has been developed in recent decades. However, the influence of LC3 on sulfate attack resistance has not been fully evaluated. Therefore, this study investigated the efficiency of LC3 mortar mixtures against sulfate attack at an early age (approximately 4.5 months) after two different curing periods, namely 1-day and 3-day curing, since the strength of the LC3 mixture is lower than OPC mixtures. To evaluate the synergistic effect of a combination of LC3 and GGBFS on the sulfate resistance, the LC3 and OPC mixtures containing 25% GGBFS were also assessed in terms of density, porosity, compressive strength, volumetric expansion, and weight changes. The experiment results show that the expansion of the LC3 mixture regardless of the addition of GGBFS and an initial curing strength made a plateau after a rapid increase up to 7 days, while the expansion of the OPC mixture kept increasing throughout the period. Furthermore, the addition of GGBFS to OPC or LC3 mixture provides the synergistic effect on reducing the expansion due to sulfate attack. Therefore, if LC3 mixture has high initial strength (min. 15 MPa) and dense microstructure to minimize the penetration of sulfate ion into the mixture, it is expected that LC3 mixture is more efficient than OPC mixture against the sulfate attack.

Abstract: Dune sands are poorly graded collapsible soils lacking fines. This experimental study explored the possibility of sustainable invigoration of fine waste materials in dune sand to improve the geotechnical properties. The fine wastes used in this study are reservoir sediments and marble waste powder. The fine waste powder was mixed with dune sand at different percentages (5, 10, 25, 50%) to study the gradation, void ratio and, compaction characteristics. A machine has been manufactured to elucidate the maximum void ratio using a developed and manufactured linear-axis 3D clay printer arm. The geotechnical properties of sand-waste mixes delineated in this study reveals the enhancement in compaction and gradation characteristics of dune sand. According to the results, the binary mixture of dune sand with 25% of marble waste and 50% of reservoir sediment gives the highest maximum dry density. Thus, for improving dune sand’s geotechnical characteristics, the addition of fine marble waste and reservoir sediment to the dune sand is an environment-friendly solution.

Abstract: In this study we investigate the addition of short polypropylene (PP) fibers in cement mortars for a wide volume percentage range. These fibers are dispersed easily in fresh mortar and create a dense network, whereas have as result the cracking reduction during dry shrinkage and the improvement of post peak response. A modified superplasticizer by lignosulfonate polymers basis was used, that keeps at low level the water to cement ratio and thus resulting to an improved mortar’s workability. Compressive strength, three-point flexural strength, drying shrinkage of hardened mortar, flow table test and air content of fresh mortar were studied in a range of volume percentages. The experimental response according to volume percentage was approximated by suitably attached theoretical models. The comparison of the obtained experimental values was done with unreinforced specimens as reference samples. From results elaboration it is concluded that the addition of PP fibers in cementitious mortars improves mortars post-peak response but weaken their compressive and flexural strengths and worsen their workability.