H.Y. Ghorab

Studies on the stability of the calcium sulfoaluminate hydrates. Part 1: Effect of temperature on the stability of ettringite in pure water

Abstract The stability of the ettringite phase in relation to its solubility in pure water has been studied at 30°, 60° and 100° for a time interval of 14 days. Ettringite is stable up to 60° in a solution of a pH value around 11. Its solubility increases with temperature. It converts to the low sulfate form after one hour boiling which decomposes further to gypsum after 14 days. Gypsum appears first when the pH of the solution is lowered to 9 and the aluminium concentration clearly decreases.

EFFECT OF MIXING AND CURING WATERS ON THE BEHAVIOUR OF CEMENT PASTES AND CONCRETE. PART 1: MICROSTRUCTURE OF CEMENT PASTES

Abstract The influence of Sea, ground, Nile and drinking waters on the microstructure of some hydraulic cements is investigated by means of X-ray diffraction analysis. The calcium sulfo- and carboaluminate hydrates form well with a water cement ratio of 2. Seawater leads to the precipitation of gypsum. The hydration products of ordinary portland cement (OPC) pastes hydrated for a year with the four water types are similar. A survey on the analysis of waters used is given.

Surface and bulk properties of ancient Egyptian mortars, part II: Adsorption and infrared studies

Abstract Adsorption studies carried out on Ancient Egyptian mortars suggest that these materials are essentially nonporous with a certain degree of mesoporosity. Analysis of the adsorption data was achieved by means of two reference nonporous materials. Surface activity is observed as a result of heat-treatment. Infrared studies confirm that the samples contain gypsum, calcite and quartz sand with a clearcut predominance of gypsum in the mortars extracted from the Sphinx statue. A correlation is perceived between these results and the X-Ray Diffraction results obtained in Part I of this series.

Effect of mixing and curing waters on the behaviour of cement pastes and concrete Part 2: Properties of cement paste and concrete

Abstract The effect of natural waters on the setting time of some hydraulic cements and on the compressive strength of the corresponding concrete is investigated. The setting time of ordinary portland cement is most affected by the water type followed by the sulfate resisting cement; the mixed cement (El-Karnak) and the portland blastfurnace slag cement are quite insensitive. The compressive strength of plain concrete cubes aged up to 17 months is unaffected by the type of mixing and curing water.

The Role of Sodium Hydroxide in the System C 3 A-CaSO 4 -H 2 O at 30°C

The hydration reaction of C 3 A with gypsum (molar ratio = 1:1.5) has been studied in water and in sodium hydroxide solutions at 30°C. The hydration product were analyzed microscopically and by means of X-ray diffraction. The concentration of sulfate and aluminum in solution was determined spectrophotometrically. In the absence of alkali, the amount of ettringite formed passes through a maximum and is accompanied by almost complete consumption of sulphate ion in solution. Alkali depresses the formation of ettringite and accelerates that of calcium hydroxide. The monosulfate hydrate appears immediately in alkaline solutions and water then reappears after a day as a solid solution with the tetracalcium aluminate hydrate. The formation of the monophase solid solution is accompanied by the consumption of C 3 A, ettringite, and calcium hydroxide and by an increase in the amount of the dissolved aluminum. The presence of alkali markedly increases the initial sulfate ion concentration from solution.

The effect of bituminous emulsion on the sulfate resistance of cement pastes

Abstract The effect of a commercial bituminous emulsion on the sulfate resistance of ordinary portland cement pastes is investigated. The behaviour of the hardened pastes in 5% magnesium sulfate solution is compared with that of samples containing up to 15% by weight of the admixture as well as that of the sulfate resisting cement. The emulsion has no effect on the rate of decrease of the sulfate and magnesium ions from the exposing solution and favours the ettringite formation in hardened ordinary portland cement pastes. A concentration of 1% increases the compressive strength of the samples but increasing concentrations accelerate their deterioration during an exposure time of six months.