Development of Environment-Friendly Concrete through Partial Addition of Waste Glass Powder (WGP) as Cement Replacement

This paper presents the study carried out on the utilization of Waste Glass Powder (WGP) as supplementary cementitious material in concrete. The evaluation of the influence of WGP on the mechanical properties of concrete was carried out by casting and testing of concrete samples as per ASTM standards (cylinders and beam elements). The control samples were designed to represent field conditions with a target compressive strength of 20,000 kPa. The Portland cement in concrete was substituted with WGP in proportions of 0%-35% by weight, in increments of 5%. Two curing domains were adopted in the preparation of the test samples to evaluate the effect of pozzolanic material wherein the tested samples were cured for 28, 56, and 84 days. The study results indicated a reduction in compressive strength of concrete up to 10% with partial replacement of cement with 25% of WGP when standard curing of 28 days was adopted. Furthermore, with the same replacement proportion and prolonged curing for 84 days, the gap in strength reduction was reduced by 5%. However, a significant decrease in workability was noted between the control concrete samples and glass powder infused concrete. Furthermore, the Waste Glass Powder Concrete (WGPC) exhibited an improved flexural strength with the modulus of rupture for WGPC being 2% higher than control concrete at the age of 84 days. Based on the results of this study it was concluded that 25% replacement of cement with WGP provides an optimum replacement ratio. Doi: 10.28991/cej-2020-03091620 Full Text: PD

Experimental Study on the Structural Behavior of Cast in-situ Hollow Core Concrete Slabs

An experimental work has been carried out to study the flexural behavior of cast in-situ hollow core reinforced concrete (HCRC) slabs constructed by using easy, cost effective and implementable techniques in field. The precast elements made of different easily available affordable material i.e. concrete, polyvinyl chloride (PVC) and plaster of paris having voided cross- sections of circular, rectangular and triangular shapes were incorporated in one direction during pouring of concrete with minimum flexural reinforcement to construct HCRC slabs. A total of 14 slab specimens including 02 specimens per specification were tested with third point loading for the assessment of flexural behavior as per ASTM standards C78/C78M. The flexural behavior of HCRC slabs with polyvinyl and plaster of paris elements having hollow cross-sections was comparable with the control solid slabs, however, HCRC slab with concrete pipes showed 7 to 8 percent reduction in flexural strength with 19 to 20 percent reduction in self-weight. All the tested specimens performed well in shear as no shear failure was observed. This study reveals that HCRC slabs with locally available material having hollow cross section elements can be used for the construction of cast in-situ monolithic construction of one-way slabs with ordinary construction techniques. Doi: 10.28991/cej-2020-03091597 Full Text: PD

Analysis of Deficient Reinforced Concrete Beam-Column Connections using Scissors Model

International audienceMacro-modeling techniques have been proved as suitable solutions for analysis and assessment of deficient reinforced concrete (RC) beam column joints subjected to seismic loads. The techniques vary from single rotational spring at the joint panel to multi-spring complex joint elements for individual response prediction at the panel and interface. The technique is used to bridge the gap between the rigid joint modeling leading to compromised structural safety and economy and finite element methods (FEM) resulting in very high computational effort. Joints built prior to development of seismic specifications exhibit certain deficiencies characterized by improper construction, weak materials, lack of transverse reinforcement, and lower reinforcement ratios. Deficient joints exhibit a brittle behavior when exposed to lateral loads

Use of Rice Husk Ash as Partial Replacement of Cement in Sandcrete Blocks

This paper presents the outcome of a research study aimed at the performance evaluation of rice husk ash as partial replacement of cement in sandcrete blocks used as masonry units. Rice husk from rice cultivated in the North of Pakistan was used in the study. It was first combusted in a locally manufactured incinerator to convert it into rice husk ash (RHA) and then finely ground to powder form for use with cement. Blocks of size 305 mm×203 mm×152 mm were molded with 0, 10, 30, 40 and 50 % replacement of cement with RHA to find compressive strength at 3, 7, 14 and 28 days age of curing. The results showed that water requirement for the required workability of the sandcrete increased with increase in RHA content whereas compressive strength decreased with increase in RHA content. However, the comparison of compressive strengths of RHA sandcrete blocks with the strength of commercial concrete blocks available in the market and used as masonry units in Pakistan showed that sandcrete blocks having sand to binder ratio of 1:8 and using up to 40% of RHA as replacement of cement gave larger compressive strength than that of commercial concrete blocks and only marginally lower strength for 50% replacement

Evaluation of Mechanical Properties of Lightweight Concrete with Pumice Aggregate

This paper presents the findings of a study carried out for evaluation of the mechanical behavior of lightweight concrete. Pumice, a rock resulting from cooling of lava, having entrapped air bubbles, has been used as a light- weight coarse aggregate. Evaluation of the mechanical behavior of the Pumice Lightweight Aggregate Concrete (PLWAC) has been carried out in comparison with the conventional concrete while comparing the mechanical properties of the two. Complete replacement of the coarse aggregate by volume had been carried out in the PLWAC. The testing regime consisted of conducting laboratory tests on concrete samples for evaluation of the mechanical properties including compressive strength, tensile stength, workability and dry density. It was concluded from the results that the use of lightweight aggregate resulted in a reduction in workability, as indicated by the slump test. Moreover, the dry density of PLWAC was also reduced by 30% as compared to the conventional concrete. A significant decrease (49%) in the compressive strength of PLWAC as compared to conventional concrete while a minor difference was observed in the tensile strenght of the two (2.9%). Based on the results of this study, it is recommended that PLWAC cannot be used in structures subjected to heavy loading conditions. However, PLWAC has a good potential to be used in low-cost structures with accompanying benefits of weight reduction

Enhancement of Confinement in Scaled RC Columns using Steel Fibers Extracted from Scrap Tyres

Steel fibers are widely extracted from scrap tyres, causing environmental concerns. This paper presents the use of steel fibers in variable proportions extracted from scrap tyres. The enhancement of the confinement was envisaged through the addition of steel fibers obtained from scrap tyres. The study included an experimental program for the development of constitutive material models for ordinary Portland cement (OPC) concrete and concrete with added steel fibers. A mix design was carried out for OPC, targeting a compressive strength of 3000 psi. Steel fibers were added to OPC in ratios of 1.0% to 3.0%, with an increment of 0.5%. Concrete columns, with cross-sectional dimensions of 6 × 6 inches and a length of 30 inches, were cast with both OPC and fiber-reinforced concrete. The column confinement was evaluated with a different spacing of ties (3- and 4-inch center-to-center). Compression tests on the concrete columns indicate that the addition of steel fibers to a concrete matrix results in an appreciable increase in strength and ductility. Overall, increasing the percentage of steel fibers increased the compression strength and the ductility of concrete. The maximum strain in the concrete containing 2.5% steel fibers increased by 285% as compared to the concrete containing 1% of steel fibers. An optimum percentage of 2.5% steel fibers added to the concrete resulted in a 39% increase in compressive strength, accompanied by a significant improvement in ductility. The optimum content of steel fibers, when used in confined columns, showed that confined compression strength increased with the addition of steel fibers. However, it is recommended that additional columns on the basis of the optimum steel fiber content shall be tested to evaluate their effectiveness in reducing the stirrup spacing

The effect of COVID-19 on the air pollution in urban areas of Pakistan

Background: The impacts of lockdown on air pollution have been examined in various parts of the world. The concentration of main air pollutants has been decreased owing to a decline in anthropogenic activities like fossil fuel burning, etc. The main aim of this research was to assess the impacts of lockdown on air pollution of the main urban areas of Pakistan. Methods: The present study was conducted to assess the air quality index (AQI) of the main urban areas of Pakistan based on the pre- and post-lockdown effects and mortality rate due to coronavirus disease 2019 (COVID-19). Hotspot analysis was conducted to assess the most vulnerable spots at the country level. Results: The AQI greatly improved in all the main cities of Pakistan which ranges from 51 to 87. The pre- and post-lockdown AQI were categorized from unhealthy for sensitive groups to hazardous and moderate, respectively. There are noticeable hotspots in the vicinity of Lahore and Karachi. The level of nitrogen dioxide (NO2) dropped 45%, 49%, 20%, 35%, and 56% in Peshawar, Lahore, Multan, Karachi, Islamabad, and Rawalpindi, respectively. Conclusion: Nature healed due to lockdown, which is the only good face of the COVID-19 pandemic. The temporary lockdown greatly improved air quality which may stimulate the policymakers, researchers, and governments for the smart use of resources to minimize emissions to heal the nature. The present study also suggests the application of hotspot analysis in different contexts for the evidencebased care services decisions during the COVID-19 pandemic. Keywords: Nitrogen dioxide, COVID-19, Air pollution, Disease outbreak

Utilization of waste marble powder as partial replacement of cement in engineered cementitious composite

AbstractThe current study focuses on the utilization of Marble Waste Powder (MWP) as a partial substitution of cement along with local sand instead of microsilica sand in Engineered Cementitious Composite (ECC). The aim was to reduce the environmental concerns of ECC by reducing the cement content without adversely affecting the desired properties. Four mixes were evaluated; the control mix which has no MWP and three test mixes having cement replacement with MWP by 10%, 15%, and 20% were used, respectively. The properties of ECC mixes were found in terms of compressive, tensile, and flexural characteristics. The trend of change in the basic properties of ECC with an increased percentage of MWP as partial substitution of cement was found along with the hypothesis test on the experimental data. From this study, it was concluded that the increased percentage of MWP reduces on the compressive strength of ECC. The maximum reduction in compressive strength of ECC was recorded as 49% with 20% replacement of cement with MWP, as compared to the control sample at 91 days of test age. The tensile strain of ECC increases with the increase in MWP content, while the tensile stress increases only with the increase of MWP content up to a specified limit. The ultimate load in the force–deflection curve first increases with the increase in MWP content up to a certain percentage, while upon further increase in MWP content from 15% to 20%, the ultimate load decreases. The study suggests that the properties do not vary significantly for the modified ECC samples containing MWP, especially the 10% and 15% MWP samples, and can be utilized instead of normal ECC, thus mitigating environmental concerns without compromising the ECC’s performance