Applied Mechanics and Materials Vol. 377

Abstract: The purpose of this study is to investigate the effects of fly ash/slag ratio and liquid/binder ratio on strength of alkali-activated fly ash/slag (AAFS) mortars. Three liquid/binder ratios of 0.35, 0.5 and 0.65 and three fly ash/slag ratios of 100/0, 50/50, and 0/100 were selected as variables to design and produce mixes of AAFS mortars. The compressive strength and flexural strength of alkali-activated fly ash/slag mortars were discussed and compared with reference mortars produced using ordinary Portland cement (OPC) mortars. Based on the results, both fly ash/slag ratio and the liquid/binder ratio are significant factors influencing the strengths of AAFS mortars. The strength of AAFS mortars except alkali-activated fly ash mortars is higher than that of OPC mortars. When the fly ash/slag ratio reaches 50/50, the AAFS mortars possesses the highest strength compared with the other mortars.

Abstract: High temperature testing of cement mortar containing bottom ash (BA) generated by municipal solid waste incineration (MSWI) as partial replacement of natural aggregate is presented in the paper. The measurements of mechanical properties, bulk density, matrix density, and total open porosity are performed on samples exposed to the temperatures of 20°C to 1000°C. TGA analysis is performed as well. Finally, the studied samples are analyzed by IR spectroscopy in order to evaluate TGA data. The obtained results indicate a comparable performance of the mortar modified by BA with the reference material.

Abstract: Clay as natural pozzolan is found in the north of the city of Sebha, Libya. Sebha clay is relatively high in silica, and its physical and chemical properties could be referred to as ASTM C618 class N. Sonication treatment is carried out and the treated Sebha clay is used as a mineral admixture in the Portland cement mortar. Horn method 20 kHz frequencies with different powers and different times are used in the Sonication treated. The particle size distributions (PSD) and Scanning Electron Microscope (SEM) imaging are used to understand the mechanism of pozzolanic improvement of the Sebha clay after treatment by sonication. This paper shows the physical and chemical properties of sonication treat Sebha clay. The effect of magnitude of sonic power on pozzolanic activity of treated kaolin is investigated. The main aim of the present research is to study the strength characteristics of cement mortar using Sebha natural clay after sonication is treated as a partial replacement of ordinary Portland cement OPC. The parameters are investigated, including compressive strengths .The results show enhancement in particle size and pozzolanic activity of treated kaolin, with increase in sonic power and in the time.

Abstract: A kind of non-alkali high efficiency liquid cement setting accelerator named ZJ-NSA was developed by regulating the chemical composition of polymerized aluminum sulfate in this paper. The results show that the initial setting time and the final setting time are sharply shortened to 2 minutes 48 seconds and 4 minutes 37 seconds respectively, and the 1 d-aged compressive strength reach to 8.6MPa when it is mixed into P.O42.5 Portland cement with 5% addition; meanwhile, its compressive strength and bending strength retention at the age of 1d and 28d reach to 79.63%, 81.89% and 78.13%, 97.89% respectively. Phase characteristics on the hydrated cement specimens by means of x-ray diffraction (XRD) and differential scanning calorimeter (DSC) were analyzed and the acceleration mechanism was discussed.

Abstract: A low temperature sulfate attack research was carried out to investigate the effects of fly ash on thaumasite form of sulfate attack (TSA) in cement-based materials. Cement-limestone-fly ash samples were immerged in 5% magnesium sulfate solution at (5±2) oC. The appearance of samples was observed, and strength was also tested. Besides, the corrosion products were analyzed by infrared spectrum (IR) and X-ray diffraction (XRD) methods. Cement was equally replaced by fly ash with 20%, 30%, and 50% proportions. The results show that: Effects of fly ash on TSA were closely related to the composition, content and fineness of fly ash. Fly ash with an activity index larger than 80% could improve the resistance to TSA in cement-based materials when the replacement reached 50% while fly ash only played a minor role in early stage with 20%-30% content.

Abstract: Application of ultrafine fly ash grinded by low quality fly ash in commercial concrete was studied, and the studied content included fineness test, mortar strength, concrete strength, admixtures adaptability, impermeability and dry shrinkage. Results show that ultrafine fly ash grinded by low quality fly ash had a very good activity and admixtures adaptability, can greatly improve the strength and impermeability of concrete, and reduce dry shrinkage, and has good applicability in commercial concrete.

Abstract: Shrinkage of repair material is the major factor inducing cracking in concrete repairs. Induced cracks in repair materials are due to restrained shrinkage. The ring test is commonly used to assess the potential for restrained shrinkage induced cracking due to its simplicity and versatility. The restrained ring test is becoming widely used as a standard test method to assess the potential for early-age cracking in concrete. In this investigation, a ring test set up was developed to measure the restrained shrinkage of various repair materials available in the local market. Keeping in view the importance of the local environment, two environment conditions were used; Lab Environment (Temperature 23±2°C) and the open environment of Riyadh. These environmental conditions were used taking into account the local environmental conditions. The samples were outside for almost one year and encountered all weather conditions of Riyadh. It has been observed that some materials although manufactured by highly reputed companies didnt comply fully in restrained shrinkage tests.

Abstract: Analytical models for compressive strength and tensile strength of high performance concrete are presented. High performance concrete was developed using binary and ternary blending combinations consisting of ordinary Portland cement, pulverised fuel ash and silica fume. Pulverised fuel ash and silica fume were incorporated as partial cement replacements for the preparation of various combinations of blended systems. Compressive strength and tensile strength of concrete containing ordinary Portland cement, pulverised fuel ash and silica fume at various ages are reported. Based on the experimentally obtained results, analytical prediction models were developed. These models enabled the establishment of isoresponse contours showing the interactive influence between the various parameters investigated.

Abstract: Objective: Measure and study the mechanical properties and abrasion resistance of recycled aggregate concrete in order to provide experimental basis for the application of recycled aggregate concrete in engineering. Method: Use recycled aggregate concrete with replacement ratio of recycled coarse aggregate respectively for 0%, 30%, 50%, 80% and 100% to do the slump, compressive strength, modulus of elasticity and abrasion resistance tests on them. Result: The workability of concrete decreases with the increase of recycled coarse aggregate content. Mechanical properties of concrete change as the replacement ratios of recycled coarse aggregate change. Conclusion: The recycled aggregate concrete and natural aggregate concrete have similar abrasion resistance. The recycled aggregate concrete can be applied in engineering.

Abstract: In the present paper, controlled rolling and controlled cooling of Fe-C-Mn-Si multiphase steel was conducted by a laboratory hot rolling mill. The results show that ferrite (grey), granular bainite (black) and retained austenite (white) and/or MA islands (white) are observed in a color etched LOM micrograph. The presence of the retained austenite is confirmed by SEM observation. Controlled rolling and controlled cooling technology contributes to the improvement of the microstructure. Excellent mechanical properties for Fe-C-Mn-Si multiphase steel are attributed to the TRIP effect of the stable retained austenite.