ICE - Institution of Civil Engineers - Virtual Library

The final composition of cement is of great importance for both the manufacturer and the consumer, since the behaviour of the cement and its application depend largely on it's composition. The composition of cement in turn, depends heavily on the raw materials, the geological origin thereof and the manufacturing process. In previous research, the major element composition of cement has been well-characterised, but the minor and trace element composition in many cases has not. This investigation is an attempt to analyse some of the materials comprising cement, cement clinker and gypsum, for a suite of trace elements that will provide a unique fingerprint of the final product. It was found that for both the clinker and the gypsum a suite of trace elements can be successfully employed to uniquely characterise the materials. The contribution of such a fingerprint is that it can provide valuable information in the case of a forensic analysis for discrimination purposes and also predict the behaviour of these species with regard to their immobilisation in a cementitious matrix.

The total strain and strain recovery-time response of hardened cement paste subjected to a sustained load was followed using impedance spectroscopy. An immediate increase in the high-frequency arc diameter on removal of the load was interpreted in terms of microstructural behaviour. The nature of the strain recovery characteristics was observed to be strongly dependent on the water=cement ratio. Aspects of a strain recovery mechanism based on readsorption of water on unloading are discussed.

The heat evolution in three high-replacement composite cement pastes—that is, Portland cement mixed with 75% and 90% ground granulated blast furnace slag and 75% pulverised fuel ash, alongside a 100% ordinary Portland cement, has been followed using isothermal conduction calorimetry at 35°C. The effects of adding 0·1% and 1% SnCl₂.2H₂O and SnCl₄.5H₂O on their heat outputs have also been studied. Results indicate that there is a significant difference between the Portland cement and the three composite cements in terms of their heat output. The addition of tin chlorides also causes complex changes to the setting times and heat output of the various cements.

Recent research has shown that a state-of-the-art process for high-performance (HP) cement adds a new dimension to ‘classical’ cement technology. The key idea of the process involves the mechano-chemical activation of cement at the grinding stage. A silica-based complex admixture is used for the activation of the cement imparting high strength and improved durability to mortars and concrete. This paper describes the effect of different complex admixtures on the strength of HP cement. According to the available results, mortars based on HP cement possess a compressive strength of up to 148 MPa. A comparison of alternative evaluation methods helps to recommend the test procedure for HP and high-strength cement.

This paper examines the corrosion of alkali-activated blast furnace slag cement in pH 3 nitric acid, pH 3 acetic acid, 30% CaCl₂ solution and 15% CO₂ atmosphere at relative humidity of 52%. ASTM Type I Portland cement is used as a reference. Experimental results indicate that alkali-activated slag pastes are corroded more slowly than Portland cement pastes in these acid and salt solutions. Alkali-activated slag pastes are carbonated very quickly during an accelerated carbonation test because of shrinkage cracking, while no carbonation can be detected on Portland cement pastes after 75 days of exposure to 15% CO₂ at a relative humidity of 52%. Detailed analyses indicate that all these differences can be attributed to the difference in hydration products in the two types of hardened cement pastes.

This paper reports the results of investigations on the chloride diffusivity of volcanic ash (VA) blended hardened cement pastes with varying curing age of up to one year. The pastes had 0, 20 and 40% VA as cement replacement by mass and water/binder ratios of 0·40, 0·50 and 0·60 by mass. The ACID test was used to calculate the chloride ion diffusion coefficient D_i , of pastes using the Nernst–Plank equation for steady state conditions. In addition, electrical resistivity, mercury intrusion porosimetry, and differential scanning calorimetry (DSC) tests were also conducted. Good correlations were found among D_i , total pore volume and electrical resistivity of the pastes. The D_i of VA blended pastes was within the range of 10⁻⁷ and 10⁻⁹ cm²/s. It was also found that blending cement with VA significantly reduced the long-term chloride ion diffusion coefficient and hence increased the long-term corrosion resistance of pastes. This fact was also supported by the presence of lower quantity of Ca(OH)₂ and higher quantity of Friedel's salt in the VA blended pastes as observed from the DSC tests. Pastes with 40% VA showed better performance in terms of chloride ion diffusivity. W/b ratio was also found to affect the D_i at the early ages of curing, but became less important at the later ages of curing.