ICE - Institution of Civil Engineers - Virtual Library

Preliminary studies on the effects of autoclaving cellulose fibre pulp used in fibre-cement building materials were conducted by Fourier transform infrared. Autoclaving at 180°C at different times in tap water showed little spectral differences. The use of lime solution under the same condition showed significant spectral differences in the regions of 3020 to 3800 cm⁻¹ and 800 to 1600 cm⁻¹. The former is the region corresponding to O—H stretch where the differences are the result of variations in the hydrogen bonding. The differences in the latter region correspond mainly to C—O stretching modes in COH and the acetal O—C—O—C groups. These results are rationalised in terms of susceptibility of the cellulose fibres to alkaline hydrolysis and oxidative alkaline hydrolysis under high temperature autoclaving conditions. Results from differential scanning calorimetry and environmental scanning electron microscopy also showed similar trends, confirming that only under the adverse alkaline and autoclave environment does the cellulose undergo significant degradation.

The present paper reports on the lead stabilisation capacity of certain new containment systems, in which fly ash from steam power plants is activated (made to set and harden) with high-alkalinity solutions. Lead is immobilised in such systems because it is precipitated as a highly insoluble silicate. Results are reported from various leaching trials conducted to determine the amount of lead fixed by activated fly ash systems. Finally, the nature of the initial fly ash is another factor found to have a significant impact on the effectiveness of lead fixation in these systems.

Day by day the increase in environmental pollution is playing a major role in the corrosion of concrete reinforcement, requiring researchers to focus on its prevention. Among the various corrosives, chloride ions produce major impact by virtue of their small size, high penetrating power, mobility and low activation energy for depassivation. The present research work is aimed at reducing the free chloride content in concrete using lead oxide as an admixture. Different proportions of admixture, varying between 5% and 20% (by weight), with regular increments of 5%, were adopted for concretes with varying curing times (3–28 days). An optimum percentage of chloride reduction was arrived at based on these proportions. The experiments revealed a 13% reduction of free chloride in cement grout and a 35% reduction in concrete with the lead oxide admixture. An increase of 30–60% in compressive strength was also observed for varying curing periods. This admixture, being economical compared with other admixtures such as zirconium oxide and titanium oxide, was found to reduce a higher amount of free chlorides, making it a feasible admixture to adopt. It can be concluded that lead oxide may effectively reduce the free chloride content in concrete, thereby reducing the risk of reinforcement corrosion.

In this paper, the formation and development of expansive stress in hardened cement paste (HCP) was studied theoretically, based on the principles of chemical thermodynamics and elasticity mechanics. The expansive stress in HCP was measured by a special test. Using both theoretical and experimental results, the disruption produced by the expansive stress caused by the expansive constituent in cement in HCP is discussed. The effects of free lime on the expansion behaviour of HCP were studied at ambient temperatures. It was found that the expansion behaviour of HCP reflects its inner stress match, which is not only relative to the content and the reactivity of expansion constituent, but also to the cohesive stress of HCP.

Steel fibre (8 μm diameter, 0·72 vol.%)-reinforced cement was found to be effective for resistance heating. A DC electrical power input of 5·6 W (7·1 V, 0·79 A) resulted in a maximum temperature of 60°C (initial temperature = 19°C) and a time of 6 min to reach half the maximum temperature. Efficiency of energy conversion increased with time of heating, reaching 100% after 50 min. The heat power output per unit area was 750 W/m² for steel fibre cement, compared with 340 W/m² for a metal wire with the same resistance. The use of carbon fibres or graphite particles in place of steel fibres resulted in less effective heating, due to the higher resistivity.

Electrically conductive cement-based materials are useful for electrical grounding, lightning protection, resistance heating, static charge dissipation, electromagnetic interference (EMI) shielding, cathodic protection, and thermoelectric energy generation. The science and applications of electrically conductive cement-based materials are reviewed. In addition, a comparative study of the effectiveness of various electrically conductive admixtures (discontinuous forms of steel and carbon) for lowering the electrical resistivity of cement shows that the effectiveness decreases in the order: steel fibre of diameter 8 μm, steel fibre of diameter 60 μm, carbon fibre of diameter 15 μm, carbon nanofibre of diameter 0·1 μm, coke powder (< 75 μm) and graphite powder (< 1 μm). For EMI shielding, the effectiveness decreases in the order: steel fibre of diameter 8 μm, coke powder (< 75 μm), carbon nanofibre of diameter 0·1 μm, graphite powder (< 1 μm), steel fibre of diameter 60 μm, carbon fibre of diameter 15 μm, and steel dust of size 0·55 mm. By using steel fibre (8 μm diameter) at 0·72 vol.%, a resistivity of 16 Ω cm and an EMI shielding effectiveness of 59 dB (1 GHz) were attained. The carbon admixtures cause the absolute thermoelectric power to be more positive, whereas the steel admixtures can cause the absolute thermoelectric power to be more positive or more negative. In particular, steel fibre of diameter 60 μm at 0·2 vol.% causes the absolute thermoelectric power to be strongly negative (−63 μV/°C). Moisture loss has no effect on the absolute thermoelectric power, but increases the resistivity.