Strain rate effects for strength of geopolymer concrete

The effects of strain rate on compressive and tensile strength of fly ash based geopolymer concrete were investigated experimentally. Four mixes of geopolymer concrete using different alkaline solutions and under vary curing conditions were prepared. One mix of ordinary Portland cement (OPC) concrete was prepared for comparison. Both Quasi-Static tests using standard MTS and dynamic tests using Split-Hopkinson pressures bar (SHPB) were conducted, which were giving varying strain rate loadings from 10‾⁷ to 103 per second. The strain rate effect is presented as the ratio of dynamic compressive strength to static compressive strength (DIF). Results show that DIFs of geopolymer concrete are generally higher than those of OPC concrete at strain range of 187/s to 346/s (compression tests) and 7/s to 13/s (splitting tensile tests), respectively. This tendency is independent on loading regimes (compression or tension). This suggests that geopolymer concrete can be used as an alternative construction material to OPC concrete for the structures which has a high risk of being subjected to impact loadings.

An investigation of major factor of influence of strength gain or loss of geopolymer when exposed to 800° C

When fly ash based geopolymer mortars were exposed to an elevated temperature of 800oC, it was found that the strength after the exposure sometimes decreased, but at other times increased compared to the original strength. The aim of this investigation is to find the reason for this contrasting behaviour. Fol-lowing exposure to high temperature, residual strengths of specimens prepared with two different fly ashes, with initial strengths ranging from 5MPa to 60MPa, were investigated. The parameter that was found to have a major influence on the contrasting behaviour was the ductility of the mortars. The results indicate that the higher the ductility the lower the strength loss. This correlation is attributed to the fact that mortars with high ductility could provide higher capacity to accommodate thermal incompatibility than mortars with low ductil-ity. Beyond the particular threshold of ductility, some mortars even increased strength after the exposure, pos-sibly due to sintering.

The properties of fly ash based geopolymer mortars made with dune sand

This paper reports the properties of fly ash based geopolymer mortars made with dune sand. The geopolymer mortars of different cation type, namely sodium based (Na), potassium based (K) and a mixed Na/K, were prepared with dune sand (DS) and river sand (RS). The corresponding geopolymer pastes were also prepared. A series of tests including compressive strength, modulus of elasticity, splitting tensile strength, microanalysis (using scanning electron microscopy), porosity (using mercury intrusion porosimetry), sorptivity and air void (using section analysis method) were carried out. The results showed a strong correlation between strength and porosity of geopolymeric materials. The addition of DS had influences on the chemical compositions and physical properties of geopolymer mortars. These influences were dependent on the type of cation. Based on the results of mechanical properties, DS can be utilised as the fine aggregate for the production of geopolymer based construction material.

Compressive and flexural properties of hemp fiber reinforced concrete

The compressive and flexural properties of hemp fiber reinforced concretes (FRC) were examined in this paper. Natural hemp fiber was mixed using dry and wet mixing methods to fabricate the FRC. Mechanical properties of the FRC were investigated. The main factors affecting compressive and flexural properties of the FRC materials were evaluated with an orthogonal test design. Fiber content by weight has the largest effect. The method for casting hemp FRC has been optimised. Under the optimum conditions, compressive strength increased by 4 %, flexural strength increased by 9 %, flexural toughness increased by 144 %, and flexural toughness index increased by 214 %.

Performance of a commercial wine store with insulated concrete walls

The internal environment within an unconditioned wine barrel store, constructed from insulated concrete panels and located in south-eastern Australia, has been investigated during a summer and winter month. Average temperatures inside the store were found to be 13.7°C and 22.8°C in the winter and summer month respectively. A validated mathematical model of the store was used to investigate the contribution of the concrete walls, insulation and the wine itself to the internal thermal environment. The concrete walls were found to be the least influential.

Properties of hemp fibre reinforced concrete composites

This research is concerned with the mechanical and physical properties of hemp fibre reinforced concrete (HFRC). An experimental program was developed based on the statistical method of fractional factors design. The variables for the experimental study were: (1) mixing method; (2) fibre content by weight; (3) aggregate size; and (4) fibre length. Their effects on the compressive and flexural performance of HFRC composites were investigated. The specific gravity and water absorption ratio of HFRC were also studied. The results indicate that the compressive and flexural properties can be modelled using a simple empirical linear expression based on statistical analysis and regression, and that hemp fibre content (by weight) is the critical factor affecting the compressive and flexural properties of HFRC.

Using geopolymer to minimise metals leaching from brown coal fly ash

Fly ash is generated from combustion of brown coal in power stations. The majority of fly ash is removed by electrostatic precipitators (ESP) and finally disposed into the landfill as prescribed wastes. A method was studied to add clay materials to the brown coal fly ash in order to form the so-called geopolymer network, which is effective at stopping the metal contents from leaching, and have minimum impact to the environment. The experiments were conducted parallel on leached fly ash and dry precipitator fly ash. The ratios of fly ash and added clay materials were varied to determine the effects of different compositions on leaching rates. Both X-ray diffraction analysis and scanning electron microscopy images showed that as the percentage of fly ash was increased, the formation of geopolymer is reduced. Eighteen metals and heavy metals were targeted during the leaching tests and the leachate samples were analysed using ICP-AES and ICP-MS. It was found that the reduction of metal leaching was achieved by adding up to 60% of fly ash to form the geopolymer like structure. Significant reductions were observed for calcium, strontium and barium. Leached fly ash achieved better stabilisation than dry precipitator fly ash for major elements. It's hard to quantify its effects on trace metals leaching due to their ultra low concentration in the fly ash. The samples spiked with trace metals of lead, zinc, mercury and barium showed remarkable reduction in leaching.

Performance of ventilated hollow core concrete panel systems in Australia

Performance of advanced fabric energy storage systems has not been reported for Australian conditions. The influence pf slab thickness and air flow rate on the annual thermal load, and maximum heating and cooling demands for a typical office module using a ventilated hollow core concrete slab system has been investigated by simulation. Performance results for Melbourne are presented and comments made on other locations.

Modeling and simulation of collisions of heavy trucks with concrete barriers

On-site collision tests of full-scale concrete barriers are an important method to understand what happens to concrete barriers when vehicles collide with them. However, such tests require both time and money, so modeling and simulation of collisions by computer have been developed as an alternative in this research. First, spring subgrade models were developed to formulate the ground boundary of concrete barriers based on previous experiments. Then, the finite element method models were developed for both heavy trucks and concrete barriers to simulate their dynamic collision performances. Comparison of the results generated from computer simulations and on-site experiments demonstrates that the developed models can be applied to simulate the collision of heavy trucks with concrete barriers, to replicate the movement of the truck at the collision, and to investigate the performance of the concrete barriers. The developed research methodology can be widely used to support the design of new concrete barriers and the safety analysis of existing ones.

Dynamic simulation of collisions of heavy high-speed trucks with concrete barriers

Real vehicle collision experiments on full-scale road safety barriers are important to determine the outcome of a vehicle versus barrier impact accident. However, such experiments require large investment of time and money. Numerical simulation has therefore been imperative as an alternative method for testing concrete barriers. In this research, spring subgrade models were first developed to simulate the ground boundary of concrete barriers. Both heavy trucks and concrete barriers were modeled using finite element methods (FEM) to simulate dynamic collision performances. Comparison of the results generated from computer simulations and on-site full-scale experiments demonstrated that the developed models could be applied to simulate the collision of heavy trucks with concrete barriers to provide the data to design new road safety barriers and analyze existing ones.

Embodied energy in buildings : wood versus concrete - reply to Börjesson and Gustavsson

We analyse the wood and concrete designs of the Wälludden building described by Börjesson et al. (Energy Policy 28 (2000) 575) in terms of their embodied energy, employing an environmentally extended input–output framework in a tiered hybrid life-cycle assessment, and in a structural path analysis. We illustrate the complexity of the inter-industry supply chains underlying the upstream energy requirements for the building options, and demonstrate that higher-order inputs are difficult to capture in a conventional process analysis. Our calculations show that Börjesson and Gustavsson's estimates of energy requirements and greenhouse gas emissions are underestimated by a factor of about 2, and that corresponding greenhouse gas balances are positive at about 30 t C-eq. Nevertheless, Börjesson and Gustavsson's general result—the concrete-framed building causing higher emissions—still holds.