Peter A. Claisse

Permeability and Pore Volume of Carbonated Concrete

Carbonation is widely recognised as a significant cause of corrosion of reinforcement in concrete. However, in addition to the depassivation of the steel it has several other effects. This paper investigates the effect of carbonation on the permeability and pore structure of concrete. One of the most significant consequences of this effect is that it causes standard tests for durability to give misleading results. Suitable test procedures for the measurement of porosity and permeability were chosen from a review of the available techniques. Samples of two concrete mixes with different water/cement ratios were each prepared with both wet and dry curing and exposed in a carbonation chamber for up to 140 days. The results show that carbonation reduces the permeability and porosity and indicate the extent of this reduction. The reduction was greatest in poor quality concrete. When compared with the other effects of carbonation the reduction in permeability is seen to be similar to the reduction in electrical resistivity because this can also lead to misleading test results.

Workability of Cement Pastes

This research investigated problems that have occurred when high-range, water-reducing admixtures have been used with various cements. The literature survey showed that prior work indicated that the problems were caused by the specific surface area, sulfate morphology, and aluminate content of the cements. The experimental work involved a comprehensive analysis of 14 different cements. A full statistical analysis of the results indicated that the sulfates were not a significant factor when high-range, water-reducing admixtures were used, but the chromate content of the cement is significant.

Effect of Steel Slag and Portland Cement in the Rate of Hydration and Strength of Blast Furnace Slag Pastes

This paper presents an experimental study of the influence of steel basic oxygen slag (BOS) and ordinary portland cement (OPC) on the compressive strength and the hydration mechanisms of blended grounded granulated blast furnace slag (GGBS) pastes. The compressive strength, the mineralogical changes due to hydration, the setting times, the alkalinity of the raw materials, and the pore solution, and the volume stability were measured on binary and ternary mixes. It is concluded that the steel slag can be used as an activator of GGBS and the optimum composition of those materials was determined with a proposed parameter called “slag index.” The properties measured in blended OPC-GGBS-BOS mixes showed encouraging results to be used industrially. The mechanisms of hydration of the blended slag mixes are discussed and a hydration model of the blended system GGBS-BOS is proposed.

A STATISTICAL ANALYSIS OF THE FACTORS WHICH CONTRIBUTE TO THE CORROSION OF STEEL IN PORTLAND CEMENT AND SILICA FUME CONCRETE

Abstract The corrosion of embedded reinforcement has been measured in two series of concrete samples made with and without condensed silica fume (CSF) as a partial replacement for the cement. Three different curing regimes were used and samples were tested at three different ages. Measurements of carbonation, electrical conductivity, strength, lime content and chloride, oxygen and water vapour transport were carried out on matching samples. The results have been analysed using analysis of variance and regression to show which aspects of the materials and methods used to make the samples and which of the measured properties had significant effects on the corrosion. The way in which these effects were modified by the presence of the csf was also analysed. The statistical analysis showed that while the corrosion rate was affected by the water/cement ratio and the curing for all samples the use of CSF significantly increased the sensitivity to poor curing. Also while electrical conductivity and chloride transport were good predictors for corrosion in all of the tests the relative significance of the different predictors was very different for the CSF mixes.

Bolted joints in glulam and structural timber composites

The widespread adoption of the European design code for timber structures EC5 will facilitate a number of design options previously unsupported by British Standards. This code uses design equations that need characteristic material data, which exists for solid timber and some sheet materials, but not for the structural timber composites that were evaluated in this research. In this programme high-tensile steel black bolts have been used with solid timber, glulam and two commercially available structural timber composites } Microlam TM and Parallam TM . The results suggest that the timber composites offer similar performance to

High performance jointing systems for timber

Abstract In current timber design, member sizes are often determined by the need to have an adequate section size for jointing. The use of high performance jointing systems has the potential to achieve substantial reductions in the volume of timber used in conventional structures such as roof trusses. In this programme four different jointing systems which are suitable for large timber sections have been tested: Standard black bolts, Split ring/shear plates, resin bonded steel dowels and butt joints with uni-axial glass reinforcement. The results have shown that the shear plates and the glass-reinforced joints offered the best performance.

A VACUUM-AIR PERMEABILITY TEST FOR IN SITU ASSESSMENT OF COVER CONCRETE

The transport properties of fluids in the cover layer are the main indicator of the durability of reinforced concrete structures. Many laboratory tests exist for measuring these properties. However, there are relatively few tests that can be used on site. In this paper, the development of a new nondestructive rapid test capable of measuring the air permeability of in situ concrete is described. The new method measures the movement of gas between different holes drilled into the concrete and gives results for the permeability of the concrete and for the volume of concrete that has been tested. A pressure measuring method was developed to measure the pressure inside the concrete by using a piezoresistive pressure transducer and a data logger. Four different techniques were investigated and one preparation technique is recommended for in situ use.

Resin-injected dowel joints in glulam and structural timber composites

Abstract Structural timber composites offer higher strength and larger sections than solid timber. They are being more widely used in the UK construction industry in more highly stressed timber components and structures. In this programme of research epoxy resin-injected mild-tensile steel dowel joints have been tested in solid timber, glulam and two commercially available structural timber composites, Microlam™ and Parallam™. The results suggest that the resin-injection dowel joint is difficult to fabricate and inappropriate for use in Parallam.

OXYGEN AND WATER VAPOUR TRANSPORT IN CEMENT-SILICA FUME PASTES

Abstract Partial replacement of cement with Silica Fume (SF) has been proposed as a method of reducing the corrosion rate of embedded reinforcing steel in concrete. Experimental work has been carried out to determine the effect of the SF on the transport rates of oxygen and water in cementitious samples. By analysing the effect of different pressure drops across the samples it is concluded that the flow of oxygen is described by the Darcy equation, but the flow of water vapour is not. The different mechanisms of transmission cause the transmission rates for oxygen to be spread over a far greater range than those for water vapour with some of the SF samples almost impermeable to oxygen.

Potential for carbon dioxide reduction from cement industry through increased use of industrial pozzolans

Abstract Abstract Concrete is the most widely used material on earth, eclipsing the combined volumes of all other man made materials by a factor of ten. In terms of its embedded carbon, it is a benign product, being associated with relatively little CO2 per unit mass when compared with metals, glasses and polymers. Conversely, it is made in such vast quantities, that it is responsible for over five percent of anthropogenic CO2. Despite recent advances in kiln design and alternative, low energy clinkers, it seems likely that the greatest carbon savings from the industry are likely to be made by the inclusion of supplementary cementing materials. This article reviews some of the options currently under investigation, especially from the UK perspective, and highlights that some of the research needs to be satisfied before such materials are more widely adopted.