Effects of extended mixing processes on fresh, hardened and durable properties of cement systems incorporating fly ash.

Specifications that correspond with system performance may guarantee the addition of value. Most specifications for ready-mixed concrete address limits on discharge time and truck-drum revolution counts. These limits have been developed for conventional concrete. As the uses of supplementary cementing materials (SCMs) become ubiquitous, it is important to determine whether these specifications are applicable to SCMs, that is, systems containing fly ash. This paper presents results of the effects of mixing time and mixer revolution counts on characteristics of lab-made pastes and mortars containing 20% and 50% fly ash. Their characteristics assessed include time-variant ion concentrations, setting time, flow, compressive strength, porosity, and apparent chloride diffusivity coefficient. Results indicate that with increasing mixing time and mixer revolution counts, mixtures with a replacement of fly ash exhibit improved both fresh and hardened characteristics. When mixed for 60 min or 25,505 revolution count, the 28-day compressive strengths of mixtures containing 20% and 50% fly ash are 50% to 100% higher than the neat cement. Fly ash is suggested to adopt in the extended mixing processes of cement systems

Effects of Fly Ash Composition to Mitigate Conversion of Calcium Aluminate Cement Composites

Calcium aluminate cement (CAC) is one of the alternative cements that is widely used for special applications. However, during the hydration process degradation of CAC microstructure, the so-called hydrate conversion process, hexagonal calcium aluminate hydrate (CAH10) transforms into a cubic (C3AH6) phase, resulting in increased porosity and reduced strengths. It is known that alternative means for stabilizing the CAC conversion are conducted by introducing fly ash (FA) in CAC, where its microstructure is attributed to aluminosilicates. However, no study has yet been conducted on different FA compositions influencing CAC performance. This study aims to evaluate the effects of different compositions of FA on CACs’ fresh and hardened characteristics. Results revealed that the microstructure was denser when CAC was mixed with FA. Regarding reactivity, CAC with calcium-rich FA systems is 13% faster than the silica-rich one. The higher the density and the lower the porosity of calcium-rich FA mixtures were found compared with silica-rich FA in both micro- and macro-structures. As seen in the microscopic structure, this is due to the calcium-rich phase formation

Using recycle concrete aggregate coating agent for improving concrete microstructure and hardened characteristics

Recycled concrete aggregates (RCA) have been widely used as concrete aggregates in construction. This is due to economic and environmental benefits of using RCA in concrete. Unlike natural aggregate (NA), the use of RCA in concrete seems not promising to the users implementing it, especially in structural purposes. The RCA concrete is reported to have lower quality than NA concrete, especially when a high RCA content is used. The product improvement to ensure the quality of RCA-based concrete is needed. This work aims to examine the microstructures of different RCA concretes. A new surface coating agent has been developed to improve paste-aggregate bonding. After casting coated-RCA (C-RCA) concrete specimens with the replacement level of 30%, interfacial transition zone (ITZ) between C-RCA particle and cement paste was characterized using a Scanning Electron Microscope with Energy-Dispersive X-ray methods. Results indicated a reduction of ITZ region when using the C-RCA concrete and, consequently resulting in improved hardened performance characteristics. The compressive and flexural strengths of the C-RCA concrete were similar to the NA concrete and were higher than the RCA. The use of surface coating agent for RCA is one of the promising alternatives such that the use of RCA can be broadened in the construction industry

Adhesive properties of urea-formaldehyde resins blended with soy protein concentrate

Commercial urea-formaldehyde (UF) resin was blended with a renewable and environmentally friendly soy protein concentrate (SP) adhesive in order to reduce the emission of volatile organic compounds. The UF resin was replaced by SP in different proportions (10 wt%, 20 wt%, and 30 wt%). Rheology showed pseudoplastic behavior of UF/SP slurries, even at low SP content, caused by the entanglements between polymer chains. Nevertheless, viscosity of UF/SP slurries dropped to 100 mPa·s at high shear rate, reaching the viscosity value of the UF resin alone. Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy confirmed a chemical reaction between the two components. Shear strength in wet conditions of UF/SP blends was 29% higher than SP alone. Water extraction showed an increase of 55% in the insoluble fraction caused by the formation of methylene bridges between UF and SP. Finally, the incorporation of soy protein slurries to a ureaformaldehyde resin led to the development of adhesives with high solid content and appropriate viscosity to be used by the spray method, and environmentally friendlier than the resins currently used by the wood industry.Fil: Bacigalupe, Alejandro. Instituto Nacional de Tecnología Industrial; Argentina. Universidad Nacional de San Martín. Instituto de Investigación en Ingeniería Ambiental; ArgentinaFil: Molinari, Fabricio Nicolás. Instituto Nacional de Tecnología Industrial; ArgentinaFil: Eisenberg, Patricia. Instituto Nacional de Tecnología Industrial; Argentina. Universidad Nacional de San Martín. Instituto de Investigación en Ingeniería Ambiental; ArgentinaFil: Escobar, Mariano Martin. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Industrial; Argentin

Microcalorimetric study of the effect of calcium hydroxide and temperature on the alkaline activation of coal fly ash

The objective of this research is to know, through the flow of heat released, the effect of the addition of calcium hydroxide and the temperature on the alkaline activation of coal fly ash with a solution of sodium hydroxide. The heat flow of the samples was measured from an isothermal conduction microcalorimeter at 25, 35 and 45 °C, with percentages of calcium hydroxide between 5 and 15 mass% and concentrations of sodium hydroxide between 6 and 10 M. The data obtained were analyzed by the ANOVA technique using a response surface. Calcium hydroxide mainly supplies nucleation sites and increases the rate of reaction during the latent period. Sodium hydroxide increases the degree of reaction, the amount and rate of the reactions up to concentrations of 10 M. The time of the wetting and dissolving processes was 6 min, independent of the temperature and composition of the mixture. The maximum amount of energy released was 200 kJ kg−1, seeking to be minimal in the initial processes and maximum in the end. The calculated apparent activation energy was 361.20 ± 16.47 kJ mol−1 which reflects the importance of the temperature in the alkaline activation processes. The temperature does not significantly affect the amount of energy released, but does affect the rate and number of reactions.The authors thank the Administrative Department of Science, Technology and Innovation of Colombia (Colciencias) for the support of this study through the National Call 567 for Doctoral Studies in Colombia. Likewise, they thank the Ministry of Economy, Industry and Competitiveness of Spain for the project grant BIA2013-47876-C2-1-P, within which a part of the tests of this study was carried out.Peer reviewe