The effect of nano-silica on the performance of geopolymer concrete reinforced with polypropylene fiber

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Reducing Damage Due to Chemical Reactions in Concrete Exposed to Sodium Chloride: Quantification of a Deleterious Chemical Phase Change Formation

It has been shown that sodium chloride can react with the tricalcium aluminate (C3A) and its hydrates, leading to a formation of a deleterious chemical phase change during thermal cycling. It is believed that this chemical phase change is implicated in the premature deterioration of concrete pavements in the cold regions. This work examines the potential formation of the deleterious chemical phase change in several cementitious pastes made using different types of portland cement and supplementary cementitious materials (SCMs). The amount of the chemical phase change was quantified using a low-temperature differential scanning calorimetry. The results indicated that the formation of the chemical phase change can be reduced by using cements with low C3A content. The addition of SCMs showed different effects on the chemical phase change formation. Slag and Class F fly ash could reduce the amount of the chemical phase change due to only the dilution effect whereas silica fume could significantly reduce the amount of the chemical phase change due to the dilution effect as well as pozzolanic reactions. Adversely, the addition of Class C fly ash showed a negative effect through increasing the formation of the chemical phase change

A Study on the Properties of Geopolymer Concrete Modified with Nano Graphene Oxide

[EN] This paper reports the results of a study conducted to examine the impacts of adding graphene oxide (GO) to GBFS-fly ash-based geopolymer concrete. The geopolymer concrete’s compressive strength, thermal conductivity, and modulus of elasticity were assessed. X-ray diffraction (XRD) analysis was conducted to understand the differences in mineralogical composition and a rapid chloride penetration test (RCPT) to investigate the changes in the permeability of chloride ions imposed by GO addition. The results showed that adding 0.25 wt.% GO increases the modulus of elasticity and compressive strength of GBFS-FA concrete by 30.5% and 37.5%, respectively. In contrast, permeability to chloride ions was reduced by 35.3% relative to the GO-free counterparts. Thermal conductivity was decreased as GO dosage increased, with a maximum reduction of 33% being observed in FA65-G35 wt.% samples. Additionally, XRD showed the suitability of graphene oxide in geopolymer concrete. The present research demonstrates very promising features of GO-modified concrete that exhibit improved strength development and durability compared to traditional concrete, thus further advocating for the wider utilization of geopolymer concrete manufactured from industrial byproducts.S

Thermal insulation and mechanical characteristics of cement mortar reinforced with mineral wool and rice straw fibers

Building insulation is an essential requirement for buildings located in areas of varying temperature conditions. However, the conventional building insulation techniques accrue high cost and consume resources. This work aimed to evaluate the use of mineral wool and rice straw to improve Portland cement mortar’s thermal insulating properties. Samples of 40x40x160 mm mortar were produced with cement and sand, but varying mineral wool and rice straw constituents from 0 to 50% in weight. Water absorption, flexural and compressive strengths, thermal conductivity were performed in samples with and without mineral wool and rice straw addition.The microstructure of mortars was analyzed using scanning electron microscopy (SEM). It was observed that reinforcing mortars with mineral wool and rice straw fibers yielded a significant drop in the mortar’s thermal conductivity, improving their insulative abilities. Although the addition of fibers, in turn, deferred the mechanical performance in some mixes, however, it was not too significant or below workable standards. The performed tests prove the feasibility of adopting the selected fibers for insulating Portland cement mortars

Thermal conductivity, microstructure and hardened characteristics of foamed concrete composite reinforced with raffia fiber

Researchers have become enthralled with using natural fiber, which is a waste product from industrial processes, as an additive in cement-based materials. This is due to the fact that natural fiber is inexpensive, has principal carbon neutrality, and is obtainable in large quantities. Additionally, this fiber is made from a renewable resource. Hence it has a low density and is amenable to undergoing chemical alteration. The idea of this investigation is to discover the reactivity of raffia (raphia vinifera) fiber (RF) in low-density foamed concrete (FC). FC density of 950 kg/m3 was utilized. Workability, density, thermal conductivity, SEM analysis, compressive, bending, and tensile strengths were the parameters that were quantified and assessed. Based on the outcomes, it has been determined that the mechanical properties and thermal conductivity of FC-RF composites may be enhanced by using RF with an ideal reinforcing fraction content of 6%. Slump flow gradually decreased from 2% to 8% RF fraction content. The lowest slump flow was achieved by adding RF to the FC mixture at a fraction content of 8%. The density of FC-RF composites shows a developing tendency, likely because of the RF's comparatively high specific gravity and increasing fraction content. The addition of RF to FC considerably enhances the material's compressive, bending, and tensile strength. The optimal strength characteristics emerged when 6% RF was added to FC. Besides, the FC thermal conductivity improves as the weight percent of RF increases because the porous structure of FC with RF allows it to absorb heat

Potential of natural rubber latex in cement mortar for thermal insulating material in buildings

The improvement of cement mortar’s thermal and mechanical properties has been greatly impacted by the addition of polymeric materials. However, polymers added to mortar shouldn’t impair either its mechanical or thermal conductivity properties. The main idea of this project is to insulate buildings by reinforcing their constituent mix with natural rubber latex (NRL) to reduce thermal conductance from excessive solar radiation which causes discomfort to building occupants. Consequently, this study presents experimental findings on the influence of natural rubber latex (NRL) on the properties of NRL-modified mortar. Five varying percentages of NRL (0.5%, 1.0%, 1.5%, 2.0% and 2.5%) were added into the mortar. Properties such as thermal conductivity, water absorption capacity, compressive and flexural strengths were evaluated. In addition, scanning electron microscopy was employed for the microstructural investigation. The experimental findings demonstrated that adding 2.5% NRL to mortar increased its thermal conductivity of mortar significantly thus enhancing its insulative properties. Even though adding NRL to mortar decreased the compressive and flexural strengths of some mixes, this wasn’t too substantial nor substandard. The tests that were executed demonstrate that the NRL has a huge potential to insulate cement mortar

Residual durability, mechanical, and microstructural properties of foamed concrete subjected to various elevated temperatures

Three different densities (500 kg/m3, 1000 kg/m3, and 1500 kg/m3) of foamed concrete (FC) were tested alongside mortar with a density of 1980 kg/m3 to investigate how high temperatures affect the qualities of FC. A flow table test was used to examine the fresh qualities of the mixtures. The modulus of elasticity, ultrasonic pulse velocity (UPV), bending strength, split tensile strength, compressive strength, thermal conductivity, porosity, and appearance and colour changes at ambient temperature and after exposure to various high temperatures (100 °C, 150 °C, 200 °C, 400 °C, 600 °C, and 800 °C) were evaluated. To study the effects of varying densities, microstructure analysis was performed utilizing scanning electron microscopy and mercury intrusion porosimetry. According to the findings, the four varied densities appeared dissimilar. FC with lower densities (500 kg/m3 and 1000 kg/m3) showed signs of cracking, while FC with a higher density (1500 kg/m3) enabled for precise detection of the pore connectivity and surface spalling occurrences. High temperatures had less effect on the mortar than FC mixtures. As the temperature increased, the modulus of elasticity, split tensile strength, bending strength, compressive strength, thermal conductivity, and mass loss decreased for all the mortar and FC samples. The UPV values increased marginally up to 100 °C before decreasing. This investigation highlighted the need for additional research and code provisions that consider different innovative construction materials and FC constituent classes

Acoustic emission signal processing framework to identify fracture in aluminum alloys

Acoustic emission (AE) is a common nondestructive evaluation tool that has been used to monitor fracture in materials and structures. The direct connection between AE events and their source, however, is difficult because of material, geometry and sensor contributions to the recorded signals. Moreover, the recorded AE activity is affected by several noise sources which further complicate the identification process. This article uses a combination of in situ experiments inside the scanning electron microscope to observe fracture in an aluminum alloy at the time and scale it occurs and a novel AE signal processing framework to identify characteristics that correlate with fracture events. Specifically, a signal processing method is designed to cluster AE activity based on the selection of a subset of features objectively identified by examining their correlation and variance. The identified clusters are then compared to both mechanical and in situ observed microstructural damage. Results from a set of nanoindentation tests as well as a carefully designed computational model are also presented to validate the conclusions drawn from signal processing