Search

This paper investigates the influence of the addition of nanoparticles, namely SnO2, ZrO2 and CaCO3, at different doses on the durability and the microstructure of self-compacting mortar (SCM). Rheological characteristics were observed through mini slump flow diameter and mini V-funnel flow time. Transport properties were studied by the water absorption and capillary absorption tests. Mechanical properties were determined by the compression tests. Durability properties were examined by the electrical resistivity and rapid chloride permeability tests. Microstructure of SCMs was investigated through scanning electron microscopy (SEM). The mixtures containing nanoparticles exhibit improved transport properties, with increased compressive strengths and resistance to water and chloride ion penetration. These improvements are attributed to the compact microstructures, as the micro pore system was refined in the presence of nanoparticles. Based on fresh and hardened mortar properties, it is found that 5 wt% SnO2, 4 wt% ZrO2, and 3 wt% CaCO3 would serve as suitable replacement levels in optimizing the overall performance. An adaptive neuro-fuzzy inference system (ANFIS) was employed to predict the SCM properties. The numerical results show that the metamodels provide accurate estimates of experimental results.

This paper presents an experimental study to examine the hardened and fresh properties of self-compacting concrete (SCC) containing nano-CuO (NC) and polypropylene (PP) fibres. Slump-flow, T50 and V-funnel tests were carried out on fresh SCCs. The hardened properties of SCCs included compressive strength, flexural strength, tensile strength, water absorption and electrical resistivity were studied. Moreover, Scanning Electron Microscope (SEM) was employed in order to investigate the microstructure of the cement matrix. Results revealed that NC had a significant influence on compressive strength, water absorption and electrical resistivity of SCCs. The replacement of cement with a combination of 3% NC and 0.3% PP fibre gave better mechanical and durability performances than the other samples. However, the compressive strength reduced slightly when PP fibres were added to the concrete. SEM images illustrated that NC refined the pores of cement matrix and thus resulting in low permeability. Also, it is evident from the SEM images that PP fibres would improve the properties of SCCs by bridging across the cracks. Apparently, the inclusion of 3% NC and 0.3% PP can be considered as an appropriate combination regarding the fresh and hardened properties of concrete. Furthermore, three support vector machine (SVM) approaches were used to predict the compressive strength based on the mix proportions. The results demonstrated that the Wavelet Weighted Least Square SVM (WWLSSVM) and Least Square SVM (LSSVM) models gave more accurate prediction than standard Support Vector Machine (SVM).

This investigation aims to assess the nano-silica and silica fume effectiveness on engineering clay soils’ characteristics stabilized with cement kiln dust. Laboratory tests, including Atterberg limits, standard Proctor compaction, unconfined compressive strength, and California bearing ratio, were performed. The manufactured specimens were tested 7 and 28 days after preparation to analyze the curing time impacts on soil’s strength characteristics. Meanwhile, changes in the chemical and microstructures of soil were observed using scanning electron microscope examination and X-ray diffraction analysis. Subsequently, the mixtures were compared based on eight environmental parameters. To this end, a new environmental index was developed to consider all environmental criteria simultaneously. Afterward, three criteria, including 28-day unconfined compressive strength, environmental index, and unit price, were taken into account as sustainability criteria. Moreover, the gray relational analysis was employed to examine the mixtures’ sustainability. The results demonstrated that the amount of 1% nano-silica and 15% silica fume by dry soil weight was an optimum addition content of employed activators for enhancing the CKD-treated soil’s geotechnical properties, respectively. Furthermore, the sustainability evaluation revealed that CKD-treated soil was the most sustainable mixture. Given the sustainability effects, nano-silica addition less than 2% and silica fume to the CKD-stabilized soil can lead to propose treated soil with considerably more sustainability than cement. It is essential to highlight that the sustainability of CKD-treated soils containing silica fume was considerably more than that of stabilized soils comprising nano-silica.

This study investigated the role of the basic properties of materials in the low-temperature cracking using thermodynamic theory concepts. The Pull Off direct tensile strength test was conducted on 32 asphalt mixtures in two states of cohesive and adhesive. The statistical analysis in the cohesive failure state demonstrated that the adhesion free energy of the asphalt binder-aggregate was not effective in this cohesion failure. Also, the cohesion mode results showed that stiffness of asphalt binder has negative and cohesion free energy, specific surface area and base-to-acid ratio of the aggregate have positive effect on the low-temperature strength of asphalt mixtures.

In the present study, Compressive strength, water absorption, electrical resistivity, Rapid Chloride Permeability Test (RCPT) and Ultrasonic Pulse Velocity (UPV) tests of the hardened composites incorporating two supplementary cementitious materials: agricultural waste ash namely as rice husk ash (RHA) and nano-TiO2 (NT) in cement mortars were investigated. The interfacial transition zone (ITZ) and the microstructure were studied by using Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD) analysis, respectively. Compressive strength results showed a substantial improvement in samples containing NT and also a slight increase in mortar performance was observed by using up to 10 wt% of RHA as a replacement of cement. However, binary mixtures displayed the best results for strength development and durability. It is also seen that a combination of 15% RHA and 5% NT in mortar led to a positive contribution to durability properties. XRD analysis showed that intensity of Alite and Belite phases decreased and new peak of portlandite achieved with the addition of NT. The SEM micrographs illustrated the widespread distribution of mortars containing NT with packed pore structures which resulted in promoting of strength and durability of specimens. Consequently, the combined mixture of RHA and NT has led to the enhancement of strength and durability properties of mortars. In general, it seems that 15% RHA and 5% NT can be considered as a suitable replacement regarding to the economic efficiency and hardened properties.

This paper presents the effects of incorporating two supplementary cementitious materials: rice husk ash (RHA) and nano-alumina (NA) in polypropylene fiber (PPF) reinforced cement mortars. RHA is an agricultural waste material and thus recycling of this material has substantial economic and environmental benefits. Compressive strength, flexural strength, water absorption and drying shrinkage of the hardened composites were investigated. The interfacial transition zone and the microstructures were studied by using scanning electron micrograph (SEM) and X-ray diffraction (XRD) analysis. A slight increase in compressive strength of mortar was observed by using up to 10 wt% of RHA as a replacement of cement. However, addition of nano-alumina helped the compressive strength of mortar remain approximately equal to that of the control specimen even when 20 or 30 wt% RHA was used. Addition of polypropylene fibers resulted in significant increase in the flexural strength of the mortar specimens. It was also observed that NA and PPF could reduce water absorption by pore blocking effect. The positive interactions between polypropylene fibers and RHA resulted in the lowest drying shrinkage of the fibrous mortar containing RHA. XRD analysis showed that the intensity of Alite and Belite phases decreased and new peak of portlandite produced with the addition of NA. The addition of RHA enhanced the late strength of the cement composites. Consequently, the combined addition of RHA, NA and PPF has resulted in increasing of flexural strength and reduction in both water absorption and drying shrinkage of mortars.