Effects of Sulfate and Sulfuric Acid on Efficiency of Geopolymers as Concrete Repair Materials

Various geopolymer mortars (GPMs) as concrete repairing materials have become effective owing to their eco-friendly properties. Geopolymer binders designed from agricultural and industrial wastes display interesting and useful mechanical performance. Based on this fact, this research (experimental) focuses on the feasibility of achieving a new GPM with improved mechanical properties and enhanced durability performance against the aggressive sulfuric acid and sulfate attacks. This new ternary blend of GPMs can be achieved by combining waste ceramic tiles (WCT), fly ash (FA) and ground blast furnace slag (GBFS) with appropriate proportions. These GPMs were designed from a high volume of WCT, FA, and GBFS to repair the damaged concretes existing in the construction sectors. Flexural strength, slant shear bond strength, and compatibility of the obtained GPMs were compared with the base or normal concrete (NC) before and after exposure to the aggressive environments. Tests including flexural four-point loading and thermal expansion coefficient were performed. These GPMs were prepared using a low concentration of alkaline activator solution with increasing levels of GBFS and FA replaced by WCT. The results showed that substitution of GBFS and FA by WCT in the GPMs could enhance their bond strength, mechanical characteristics, and durability performance when exposed to aggressive environments. In addition, with the increase in WCT contents from 50 to 70%, the bond strength performance of the GPMs was considerably enhanced under sulfuric acid and sulfate attack. The achieved GPMs were shown to be highly compatible with the concrete substrate and excellent binders for various civil engineering construction applications. It is affirmed that the proposed GPMs can efficiently be used as high-performance materials to repair damaged concrete surfaces.

Effective Utilization of Industrial and Agricultural Waste for Developing Sustainable Self-Compacting Concrete

SCC (Self compacting concrete) can fill formwork and encloses reinforcing bars under gravity and maintains homogeneity without vibration. SCC shortens the period of construction, guarantees compaction in confined zones, moreover terminates noise due to vibration. The wide spread application of SCC is restricted because of the high cost for the production of SCC with high cement content and chemical admixtures. In order to make the production of SCC economical, and to reduce the high cement content the Ordinary Portland Cement in SCC can be blended with pozzolanic materials like rice husk ash and supplementary cementitious materials like fly ash. In this paper the fresh state properties and mechanical properties such as compressive strength, split tensile strength and flexural strength of SCC with ternary blends of rice husk ash (RHA) and fly ash (FA) were studied. For this purpose, different mixes were prepared by replacing Ordinary Portland Cement (OPC) with 5%, 10%, 15% and 20% of rice husk ash (RHA) and the percentage of addition of fly ash (FA) is fixed as 15% for all these mixes. It was observed that the specimen incorporating 10% of rice husk ash (RHA) and 15% of fly ash (FA) as ternary blend exhibits better mechanical properties such as: Compressive, split tensile and flexural strengths at 28 days of age as compared to traditional mix of SCC without RHA (Rice Husk Ash) and FA (Fly Ash). This research demonstrates that the ideal percentage for a mixture of rice husk ash (RHA) and fly ash as ternary blend is 10% and 15% respectively.

Equivalent CO2 Emission and Cost Analysis of Green Self-Compacting Rubberized Concrete

Global warming and climate changes are the major environmental challenges globally. With CO2 emission being one of the main greenhouse gases emitted to the environment, and cement and concrete production amounting to about 10% of the global CO2 emission, there is a need for the construction industry to utilize an environmentally sustainable material as an alternative to cement. This study analyzed the cost, CO2 emission and strength properties of green self-compacting concrete (SCC) ternary blend containing fly ash, calcium carbide residue (CCR), and crumb rubber (CR) as a replacement material by volume of cement, cementitious material, and fine aggregate, respectively. Cement was replaced with fly ash at 0 and 40% by volume. CCR was used as a replacement at 5 and 10% by volume of cementitious materials, CR replaced fine aggregate in proportions of 10 and 20% by volume. The result indicated that the mix with 0% fly ash and 20% CR replacement of fine aggregate was the most expensive and had the highest CO2 emission. However, the mix with 10% CR, 40% fly ash, and 10% CCR had the lowest CO2 emission and was therefore the greenest SCC mix. The 28-day maximum compressive strength of 45 MPa was achieved in a mix with 0% CR, 0% fly ash, and 10% CCR, while the utmost 28-day splitting tensile strength of 4.1 MPa was achieved with a mix with 10% CR, 0% fly ash, and 5% CCR, and the highest flexural strength at 28 days was 6.7 MPa and was also obtained in a mix with 0% CR, 0% fly ash, and 5% CCR. In conclusion, a green SCC can be produced by substituting 40% cement with fly ash, 10% fine aggregate with CR, and 10% CCR as a replacement by volume of cementitious material, which is highly affordable and has an acceptable strength as recommended for conventional SCC.

Alkali-Active Sand Slate Powder for Use as Mineral Admixture in Mass Hydraulic Concrete: Technical and Economic Analysis

This work has launched a comprehensive investigation on the macro performance and micro structure of mass concrete produced with alkali-active sand slate powder (ASSP) for use as the mineral admixture and a thorough analysis on its technical and economic effects is also conducted. Results indicated ternary blend with hybrid of 5–8 wt.% silica fume (SF) and 15–20 wt.% ASSP has the optimal compressive and flexural strength. ASSP particle participates in hydration, accelerates hydration of cement clinker within 8.5 hours, and reduces the autogenous strain of pastes by 164 × 10−6 in case of dosage less than 25% by mass. Improvement in the mechanical and deformation properties of concrete produced with the hybrid of SF and ASSP is attributed to better particles gradation, compactness enhancement, and transformation in products of hydration. On the whole, it provides another new approach for use of alkali-active rock after second processing as mineral admixture in hydraulic concrete in terms of good performance and economic effects.

Removal of Pb(II) ions using Chitosan oligosaccharide/carboxymethyl cellulose/kaolin clay blend

Heavy metal removal from wastewater has become a major environmental concern around the world. The performance of a chitosan-oligosaccharide-based hybrid (chitosan oligosaccharide (COS)/Carboxymethyl cellulose (CMC)/Kaolin clay (KC) ternary blend material prepared in the presence of Glutaraldehyde (Glu) ternary blend material for the adsorptive removal of lead (Pb) from waterwaste was investigated in this study. The structure of COS with amine and hydroxyl groups helps to remove Pb ions. FTIR and X-Ray diffraction were used to characterize of COS/CMC/KC + Glu blend. The removal of ions was assessed using batch adsorption studies, which varied parameters such as the influence of beginning concentration, adsorbent dose, and contact time. The elimination of Pb ions by adsorption was pH-dependent, with a maximum at pH 5. The favorability of the reported experimental values was validated using several theoretical models such as Freundlich and Langmuir isotherms, pseudo-first-order and pseudo-second-order kinetics. The Langmuir isotherm and pseudosecond-order best fitted for the adsorption.