Aerated Concrete Produced Using Locally Available Raw Materials

Aerated concrete materials were developed with abundant natural materials. Aerated concrete can provide insulating qualities complemented with secondary structural attributes when used as core in sandwich composites for building construction. A hybrid binder that comprised lime and gypsum was used. Different foaming agents were considered for production of aerated concrete, including saponin that is found abundantly in different plants. Different formulations were considered, and the stability of the foam structure as well as the density and early-age compressive strength of the resulting aerated concrete were evaluated. One formulation comprising lime-gypsum binder with saponin foaming agent, with a density of 0.53 g/cm3, was further characterized through performance of thermal conductivity, split tension, flexure, elastic and shear modulus and sorptivity tests. The results pointed at the satisfactory balance of qualities provided by the aerated concrete when compared with alternative aerated concrete materials

Alkali-Activation of Non-Wood Biomass Ash: Effects of Ash Characteristics on Concrete Performance

Combustion of biomass is increasingly practiced for power generation. Unlike coal ash, the combustion ashes of biomass do not offer significant value in Portland cement concrete production. An experimental study was conducted in order to assess the value of the combustion ashes of different non-wood biomass types towards production of alkali activated binders for concrete production. The results indicated that concrete materials with a desired balance of fresh mix workability, set time and compressive strength can be produced used alkali activated non-wood biomass ash binders. Correlations were drawn between the concrete engineering properties and different non-wood biomass ash characteristics. It was found that statistically significant relationships exist between the concrete properties and the non-wood biomass ash degree of crystallinity and solubility. These two ash characteristics were also found to be correlated. It was concluded that the suitability of non-wood biomass ash for use in production of alkali activated concrete can be assessed based on its degree of crystallinity

Potential use of Jordanian volcanic tuffs as supplementary cementitious materials

Ten Volcanic tuffs collected from several locations in the northern region of Jordan were investigated for potential use as supplementary cementitious materials. The volcanic tuffs were subjected to screening tests which evaluated their chemical composition, morphology and pozzolanic activity. The more promising tuffs were evaluated further as partial (10–40 wt.%) replacement for Portland cement. Their effects on the fresh mix workability, and hardened material strength and susceptibility to alkali-silica reactions were examined. Volcanic tuffs with higher SiO2 content produced higher early-age compressive strengths, and those with higher CaO contents produced improved long-term strength development qualities. Partial replacement of Portland cement with the selected volcanic tuffs reduced the susceptibility to deleterious alkali-silica reactions. Keywords: Natural pozzolans, Jordanian volcanic tuffs, Pozzolanic activity index, Alkali silica reaction, Zeolite, Calcium silicate hydrat

Plastic shrinkage cracking and bleeding of concrete prepared with alkali activated cement

Restrained shrinkage cracking that appears on concrete surfaces during construction, or while concrete in the curing process adversely affect the long-term durability and other performance attributes of concrete-based-infrastructures. This study investigates the effects of early-age surface cracking on restrained shrinkage concrete made of alkali activated cement. Concrete produced using this class of cement differs from ordinary Portland cement concrete in terms of surface qualities and some other properties. Bleeding which could be a main cause of plastic shrinkage cracking was measured and compared with that of Portland cement. Rheological tests were performed to gain further insight into factors that may influence the early-age performance of the cement paste. Portland cement was used as control for comparative assessment of the alkali activated cement performance. Experimental test showed that alkali activated cement improved the characteristics of the newly produced concrete. The concrete prepared using alkali activated cement has low tendency to bleeding and higher resistance to plastic shrinkage, also, the viscosity and yield stress of the alkali activated cement paste were relatively higher when compared to those of ordinary Portland cement paste. Test data collected from rheological and bleeding tests on the alkali activated cement concrete were used to explain its desired resistance to plastic shrinkage cracking

Optimization of ultra-high performance concrete, quantification of characteristic features

An optimization experimental program was designed to identify a desired balance of key mix design parameters for an economical ultra-high-performance concrete (UHPC) mixture. The following mix design parameters were evaluated: superplasticizer content, coarse-to-fine aggregate ratio and steel fiber volume fraction. The values of packing density, water film thickness and excess paste film thickness were calculated considered in the optimization experimental program. The trends in the effects of packing density, water film thickness and excess paste film thickness on compressive strength and fresh mix flow were investigated. The results were used to identify viable ranges of these defining characteristics for the category of UHPC. Response surface analysis of the fresh mix flow and the hardened concrete compressive strength test results led to identification of the optimum values of mix design parameters. The optimum mix was found to produce a desired balance of fresh mix flow and hardened concrete compressive strength