Advanced Materials Research Vols. 931-932

Abstract: New types of binders are being developed as an alternative to traditional cement. These alternatives are developed to have better properties and to be more environmentally friendly. Geopolymer is a novel binder that is produced from by-products such as fly ash, rich hushes ash and bio mass ash. In this experiment, fly ash, which was a by-product from electrical-generating power plants, was used during the synthesis of geopolymer. According to ASTM standard C168, fly ash is categorized into two types: class F and class C. This research focuses on the effects of using both types of fly ashes on mechanical properties of geopolymer. The experiment studies the changes on setting time, drying shrinkage and compressive strength of geopolymer mortar when 0, 25, 50, 75 and 100 percent of total weight of class F fly ash (LCF) is substituted with class C counterpart (HCF). The study used sodium silicate (Na₂SiO₃) and sodium hydroxide (NaOH) as alkali activators. The samples were cured for 24 hours either at an ambient temperature of 25°C or at an elevated temperature of 60°C.The result showed that the setting time of pure LCF geopolymer mortar was 6 times longer than that of the pure HCF ones. In addition to setting time, the specimens with 25 percent of their total binders weight replaced by HCF appeared to have the highest strength. However, the increase in HCF also increased the drying shrinkage by 6 and 12times when the specimens were cured at25°C and at 60°C respectively

Abstract: The objective of this work was to examine the microstructural changes caused by the carbonation of normal mortar. Samples were prepared and subjected to accelerated carbonation at 20°C, 65% relative humidity and 20% CO₂ concentration. The evolutions of the pore size distribution and the specific surface area during carbonation were calculated from the adsorption - desorption isotherms of water vapour and nitrogen. Conflicts observed in the results showed that the porous domains explored by these two methods are not the same due to the difference in molecular sizes of nitrogen and water. These two techniques therefore help to complementarily evaluate the effects of carbonation. The study also helped to explain why results in the literature diverge greatly on the influence of carbonation on specific surface area.

Abstract: An approach which combines the Latin Hypercube technique with Crank-Nicolson based finite difference approach is developed for probabilistic assessment of chloride diffusion in concrete structures with repairs. Two random variables, i.e., surface chloride and diffusion coefficient, are considered. Four repair strategies are proposed by varying the diffusion coefficient of repair concrete and the repair depth. A repair by cover replacement is applied at a critical time which the chloride content at a threshold depth reaches its critical value for concrete cracking. The critical time is defined as the repair time, which the CO₂ due to repair concrete production and replacement processing occurs. By this method, the median of repair time and the probabilistic time-dependent CO₂ can be assessed. The mean and the percentiles of cumulative total CO₂ are compared.

Abstract: In this study, mix proportion parameters of lightweight concrete (LWC) containing ethyl vinyl acetate (EVA) plastic waste from footwear manufacture were investigated by employing Taguchis method and ANOVA statistics. The mixtures were designed in a L₉ orthogonal array with four factors viz., water/cement, water content, EVA content and sand/cement. The results showed that EVA content and water/cement ratio had the significant effect on density and compressive strength of LWC. The density and compressive strength of the LWC containing EVA waste ranged from 1172 to 1441 kg/m³ and from 3.5 to 10.8 MPa, respectively. It can be concluded that the obtained LWC can be classified as masonry concrete. The best possible levels for mix proportions were determined to optimize density and compressive strength of the samples.

Abstract: This research was to study the influence of a sustained load on the electrical resistivity of a cement-based sensor. The cement-based sensor in this study was made of cement paste having water to cement ratio of 0.4 with the addition of graphite powder at 2% and 4% by weight of cement and carbon fibers at 2% and 4% by volume. The sustained load was applied on the cement-based-sensor using a sustain machine to control a compressive force continually at 30% of its ultimate compressive strength for a period of 30 days. The test results showed that the sustained load induced a creep strain on the cement-based-sensor. The graphite incorporated cement-based sensor showed higher creep strain than the plain cement-based sensor while the carbon fiber cement-based sensor showed lesser. In addition, it was shown that the creep strains affect the electrical resistivity of the cement-based sensors.

Abstract: This paper investigated the effect of clay brick powder (BP) on expansion behaviors of mortar bars using rhyolite aggregates, local volcanic rock from central Thailand. The accelerated test condition (ASTM C 1260) was used in this study. The expansion of samples with varying percentages of BP as cement replacement were compared to those of cement mortar bars. The brick powder significantly reduced expansion of mortar bars. As the percent replacement increased, the larger percentage of expansion reduction was. Due to the possible negative effects on mechanical properties of the mixture, the amount of the supplementary materials should be kept as low as possible. The mixture with 30% BP which yielded expansion below 0.05% at 14 days after acceleration, was chosen to study the effect on strength reduction, compared to the plain mixtures under normal and accelerated conditions. Compressive strength of BP samples under accelerated condition was slightly lower (approx.4%) than that of under normal curing while the strength of control mix was significant lower (of 18%) under similar conditions.

Abstract: The aim of this research was to implement cement-based sensors in monitoring the change of strain in concrete structures in particular where a compression applies. The experiment was conducted in a laboratory by embedding a cement-based sensor in a 150x150x150 mm normal strength concrete cube. When the sensor-installed concrete cube was loaded, the relation between the fractional change in resistivity (FCR) and strain of the sensors was evaluated. In this study, all cement-based sensors were made of cement paste containing carbon fiber at 2% by volume fraction. They were then varied with the addition of graphite powder at 4% and silica fume at 15% by weight of cement. Thus, there were total four mix proportions. From the experimental results, all sensors provided a good corelation between the FCR and compressive strain. Among them, the carbon fiber plus graphite powder (no silica fume) cement-based sensor yielded the most excellent piezoresistive response.

Abstract: The aim of this research is to study about physical, mechanical, and thermal insulation properties of light weight concrete block products mixed with ethylene vinyl acetate plastic scrap (EVA) from shoe factories. The ratio of cement: aggregates (quarry dust + EVA): water is 1:4.5:1.66 by weight. EVA to cement ratios (E/C) are fixed at 0.00, 0.33, 0.42, 0.50 and 0.58. The concrete block samples are cast for testing the necessary properties followed the TIS standard 58-2533. From the experiment, EVA plastic with the appropriate size and quantity are well adhesive with cement as well as quarry dust mixture. The least density of light weight concrete block mixed with waste of ethylene vinyl acetate plastic products is 640 kg/cu.m. The appropriate mixtures of light weight concrete block mixed with EVA plastic scrap can reach the required values from the standard of TIS 58-2533 and can be used as a thermal insulation wall.

Abstract: The present study evaluates potential re-use options for two different types of brown coal fly ash (class C) sourced from Australia as feedstock for geopolymer binder systems. The study covers analysis of fundamental material and mix-design requirements for geopolymer binders as a basis to achieve durable brown coal ash geopolymer matrices. The study established that reference unblended 100% brown coal ash geopolymer mortar samples yielded low strength, typically below 5MPa and poor durability. However, appropriate blends of brown coal ash with selected black coal fly ash (class F) and blast furnace slag to achieve target Si/Al ratios significantly enhanced both setting characteristics, as well as early age compressive strength development (25-35MPa) while improving overall durability performance compared to reference mixes. Moreover, lagoon fly ash blended geopolymer shows better durability while dry precipitator fails to perform well. The discussion also focuses on key source material parameters and reaction processes that influence compressive strength and durability behaviour of marginal brown coal ash sources during geopolymerisation reactions.

Abstract: The principal aim of this research is to improve the seismic performance of high strength concrete (HSC) reinforced columns using fiber reinforced concrete (FRC) by mixing steel fiber into the concrete. Two reinforced concrete columns 200mm x 300mm in cross-section with a height of 1250 mm were tested under cyclic lateral loading. The first specimen was casted using high strength concrete of 100 MPa and the second specimens were also casted using similar concrete strength but the steel fiber of 0.5% by volume was added to the concrete in the plastic hinge region. Both columns were subjected to lateral cyclic load until the failure occurs. The test results showed that the use of FRC in the plastic hinge region could significantly improve column displacement ductility. The maximum drift at column failure at 4.5% for non-ductile column could increase to 8% in FRC column. It is evident that the cracks in FRC column are much smaller properly spread in the plastic hinge region and hence the plastic hinge could be able to rotate without lateral strength being compromised. In FRC column, concrete spalling was observed in a very high drift (7%) and bar buckling occurred at around 8% drift whilst in HSC column concrete spalling and bar buckling occurred at only 3.5% and 4% drift respectively. It was evident that the use of steel fiber in HSC columns could significantly improve seismic performance of the column.