Durability in concrete : new instruments : new opportunities

New infrastructure, particularly in the developing countries, demands substantial capital investment and a loss of durability of the concrete means a waste of oportunity. Improving durability of concrete structures is a non-trivial task. The durability of concrete has been related to its ability to resist the transport of water and the potentail imporvements to concrete durability using supplementary cementitious materials (SCM) has been well documented. With access to neutron and synchrotron facilities it has become possible to; (a) measure the ability of SCM to inhibit transport of water in concrete (b) measure particle size increase of hydrating cements (with and without SCM) by ultra-small angle neutron scattering (c) use neutron tomography combined with x-ray tomography to determine the three dimensional flaws in the structure of concretes that enable water ingress into structures, and (d) determine the amount of curing or degree of hydration on the durability of SCM/OPC blends. This review will detail preliminary results on cement and concrete obtained using the newly available neutron, synchrotron and other facilities in Australia and Brazil and highlights their ability to estimate factors which determine the service life of concrete

Using x-ray powder diffraction as a cost effective tool in cement industry

Rietveld Analysis of cement diffraction patterns have been used to determined the composition of cement since John Taylor's pioneering work in the 1990's. Since then many workers have used this techniques to analyse cement and supplementary cementitious materials and their hydration products, both for research and production control purposes. Nevertheless there are a number of factors, including the amorphous content of the cement and relative proportion of mineral polymorphs present in the initial clinker, whose impact on analysis are still not completely understood. X-ray powder diffraction beamlines from the Brazilian Synchrotron Light Laboratory (LNLS) and the Australian Synchrotron, which produce more intensity and better resolution than normal x-ray diffraction sources, were used to investigate cement diffraction patterns and the hydration products of a range of cement pastes cured for up to 28 days. This study highlights the information that can be obtained from X-ray diffraction analysis for controlling and optimizing cement production and concrete durability.

Molecular depth profiling of organic and biological materials

Atomic depth profiling using secondary ion mass spectrometry, SIMS, is common in the field micro-electronics; however, the generation of molecular information as a function of sample depth is difficult due to the accumulation of damage both on and beneath the sample surface. The introduction of polyatomic ion beams such as SF₅ and C₆₀ have raised the possibility of overcoming this problem as they deposit the majority of their energy in the upper surface of the sample resulting in increased sputter yields but with a complimentary reduction in sub-surface damage accumulation. In this paper we report the depth profile analysis of the bio-polymer polycaprolactone, PCL, using the polyatomic ions Au₃⁺ and C₆₀⁺ and the monoatomic Au+. Results are compared to recent analysis of a similar sample using . depth profiling of cellulose is also demonstrated, an experiment that has been reported as unsuccessful when attempted with implications for biological analysis are discussed.

Synchrotron powder diffraction study of cements pastes

 Knowledge of the degree of hydration of cement pastes is critical for determining properties such as the durability of concrete. As part of an integrated study on the prediction of chloride ingress in reinforced concrete, synchrotron Xray powder diffraction was used to estimate the degree of hydration of cement pastes. While for the past 20 years the composition of Portland cement has been determined by Rietveld analysis of X-ray diffraction, nevertheless there are a number of factors, including the amorphous content of the cement and relative proportion of mineral polymorphs present in the initial clinker, whose impact on the analysis are still not completely understood. Analysis of the resulting diffraction patterns indicated enhanced identification of polymorphs of alite, belite, ferrite and aluminate, which are present in the initial unhydrated cement and clinker, as well as improved quantification of hydrated crystalline phases such as calcium hydroxide and ettringite, which are key phases determining the speed of the chemical reactions in cement. In this paper we describe the experience that we have gained in the determination of the degree of hydration of cement pastes. We detail the standards and precautions that we took to characterize production cements and their hydration products.

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.

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.

Sound absorption characteristics of a precast panel system made from environmentally sustainable concrete

This paper investigates the sound absorption characteristics of a precast panel system made from an environmentally sustainable concrete which can be used as an acoustical material. A current research project undertaken at the School of Architecture and Building, Deakin University, aims at utilising alternative materials and innovative approach to concrete precasting in the production of architecturally pleasing concrete panels. The normal incidence sound absorption coefficients of the assemblies were measured using an impedance tube. In general, the peak frequencies reduced with increasing thickness of concrete. The preliminary results indicate that the sound absorption of a three-layer variation of the panel meet design specifications related to acoustic performance. The major benefits of this investigated approach to concrete and concrete precasting are the ease of tunability to specific peak frequency, improved aesthetics and utilisation of industrial waste.

Debond detection in RC structures using piezoelectric materials

This paper presents a technique to detect the delamination between the steel bars and concrete in the reinforced concrete structures. The piezoelectric components are mounted on reinforcing bars that are embedded in RC structures as sensors and actuators to generate and record the signal, which is sensitive to the delamination between the steel bars and concrete. The experimental study is carried out on a concrete slab with different debonds between the rebars and concrete. The test results show that the delamination between the rebars and concrete can be detected with the embedded piezoelectric sensors and actuators.

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.

Cement-Wood composites: effects of wood species, particle treatments and mix proportion

The aim of this research was to investigate the effects of wood species, particle treatments and mix proportion on the physical (density) and mechanical (compressive strength and dynamicmodulus of elasticity) properties of cement-wood composites. Different mix proportions were investigated, based on the cement: wood ratio of 0.3:0.7, in volume, with Pinus elliottii and Eucalyptus grandis sawdust percentages of 0-100, 25-75, 50-50, 75-25 or 100-0. Sawdust particles were pre-treated with either lime or cement coating to improve cement and wood compatibility. Results show that wood species, particle treatments and mix proportions may influence the physical and mechanical properties of cement-wood composites. In general, results confirm that Eucalyptus sawdust and cement are naturally compatible and do not require any previous particle treatment to avoid compatibility problems.