Microstructure Properties Of Concrete Research Articles

Strength properties and micro-structural properties of concrete containing coal bottom ash as partial replacement of fine aggregate

The coal fired thermal power plants are the main source of production of coal ash. The coal ash collected at the bottom of the furnace is called coal bottom ash (CBA). The objective of the present research work was to explore the possibility of utilization of coal bottom ash as partial replacement of fine aggregate (sand) in concrete. Experimental tests were performed to evaluate the properties of fresh and hardened concrete containing coal bottom ash. The properties such as unit weight, compressive strength, and splitting tensile strength, modulus of elasticity and microstructure of concrete incorporating coal bottom ash in partial or full replacement of river sand were examined and compared with those of conventional concrete. Water loss by bleeding and workability of fresh concrete after replacing river sand with coal bottom ash were also examined. The test results of this research work indicate that at fixed water cement ratio, workability and loss of water from bleeding decreased with the use of coal bottom ash as a replacement of river sand in concrete. Compressive strength of bottom ash concrete at the curing age of 28days was not strongly affected. However, after 90days of curing age, compressive strength of bottom ash concrete surpassed that of conventional concrete. Splitting tensile strength of concrete improved at all the curing ages. The modulus of elasticity decreased with the use of coal bottom ash at all the curing ages. SEM and XRD studies indicated that the C–S–H gel structure was slightly less monolithic than that of control concrete and total intensity of ettringite was not changed with the addition of coal bottom ash in concrete.

An experimental survey on combined effects of fibers and nanosilica on the mechanical, rheological, and durability properties of self-compacting concrete

Previous studies have shown that application of fibers in concrete enhances scratching, flexural and tensile strength. Self-Compacting Concrete (SCC) is a highly flowable and coherent concrete able to self-compact under its own weight. On the other hand, nanosilica particles and artificial pozzolans possessing high efficiency in concrete technology can improve structural properties of cement-based materials. Previous studies have suggested self-compacting and fiber-reinforced concretes for more stable and efficient buildings. Therefore, the present study aimed to evaluate the effects of nanosilica and different concrete reinforcing fibers including steel, polypropylene and glass on the performance of concrete. In this study mechanical (compressive, splitting tensile and flexural strength, toughness and modulus of elasticity), rheological (L-Box, slump flow, T50) and durability (resist chloride ion penetration (RCPT) and water absorption) properties are assessed. In addition, microstructural properties of concrete were assessed using Atomic Force Microscopy (AFM) and X-Ray Diffraction (XRD) techniques. Totally, 40 concrete mixes , labeled as A, B, C and D, with nanosilica contents of 0, 2, 4 and 6 weight percent (wt.%) of cement, respectively and three types of reinforcing fibers (steel: 0.2, 0.3 and 0.5 volume percent (v%) and polypropylene: 0.1, 0.15 and 0.2v% and glass: 0.15, 0.2 and 0.3v%) were evaluated. The results of the study showed that the presence of both nanosilica and reinforcing fibers in optimal percentages, can improve the mechanical properties and durability of self-compacting concrete significantly.

Retained properties of concrete exposed to high temperatures: Size effect

AbstractConcrete as a construction material is likely exposed to high temperatures during fire. The retained properties of concrete after such exposures are still of great importance in terms of the serviceability of structures. This paper presents the effects of high temperatures on the physical, mechanical, and microstructural properties of concrete. Specimens with different sizes were exposed to high temperatures ranging from 200 to 1200∘C. The compressive strength, splitting tensile strength, ultrasonic pulse velocity, and rebound numbers of the specimens were determined. The microstructures of the specimens were examined by scanning electron microscope (SEM) analyses. The test results indicated that the retained compressive strength of concrete considerably decreased with increase in temperature. The effect of specimen size on the retained compressive strength was not pronounced. The retained splitting tensile strength of concrete remarkably reduced as the temperature was increased. The specimen size played an important role on the retained splitting tensile strength of concrete up to 400∘C. The test results revealed that ultrasonic pulse velocity (UPV) test can be successfully used in order to check the uniformity of fire‐damaged structures. The rebound numbers decreased with increase in exposure temperature. SEM studies on specimens exposed to 800∘C revealed significant changes in the microstructure of the concrete. Copyright © 2009 John Wiley & Sons, Ltd.