Formation Of Portlandite Research Articles

Subject index of volume 93

The consolidation of a fine-grained lateritic soil, treated with compound Portland cement (CEMII/BM 32.5 N) up to 9% by weight of the dry soil and prepared at three different molding water contents (ωDRY, OMC, and ωWET), was investigated by means of a one-dimensional consolidation test. The physicochemical and microstructural properties of the compacted lateritic soil-cement mixture were investigated using Raman spectroscopy, polarized light microscopy (PLM), scanning electron microscopy (SEM), and pH measurement. The results show that cement admixtures resulted in the formation of tobermorite, afwillite, ettringite, portlandite, and calcite. However, tobermorite and afwilite, which are calcium silicate hydrates (CSH) whose mechanisms of formation are the pozzolanic and alkali silica reactions, appear from 6% added cement. The fixing point of the pH (12.4) is also obtained from 6% added cement. It is the threshold value at which the material begins to develop an adequate mechanical performance. In general, as the content of cement in the soil is increased, the yield stress increases from 1 to 3 times in comparison to untreated soil. For effective vertical stresses smaller than the cement-induced yield stress, the primary consolidation process for specimens treated with cement is 2–7 times faster than that for specimens not treated with cement, while for effective vertical stresses higher than the cement-induced yield stress, the primary consolidation process for specimens treated with cement is about 0.5–1.5 times faster than that for specimens not treated with cement. Permeability and secondary compression are reduced 1–9 times and 2–11 times that of the untreated samples, respectively. These changes are attributed to the creation of chemical bonds and aggregation that accompany the addition of cement. The results also show that it would be desirable for soil samples to be prepared at the dry side of optimum (ωDRY) when the optimum moisture content (OMC) is not reached at the site. These results indicate that significant and desirable changes in soil behavior can be achieved when the soil is admixed with CEM II/BM 32.5 N cement, thus providing the possibility of using the tested lateritic soil in road construction.

Contribution of 1H combined rotation and multipulse spectroscopy nuclear magnetic resonance to the study of tricalcium silicate hydration

Hydration products of tricalcium silicate (C3S) are the calcium silicate hydrates (C–S–H) and portlandite. Silica fume, added to anhydrous cement in industrial formulations, reacts with portlandite and leads to C–S–H slightly different from the previous one (this reaction is called the pozzolanic reaction). C3S hydration at 120 °C with and without silica fume has been studied by two 1H nuclear magnetic resonance techniques: combined rotation and multi-pulse spectroscopy (CRAMPS) and magic angle spinning (MAS). The static spectra are broadened by the proton–proton dipolar interaction. The 1H MAS technique does not allow us to remove the effects of this interaction completely and cannot be in this case a quantitative method. Therefore the CRAMPS technique, which can remove the broadening of the interaction because of the use of a multipulse sequence associated with the sample rotation, was used. It is shown that the CRAMPS NMR spectra allow us to describe the action of silica fume on the hydrates and to reveal the competition between portlandite formation around the C3S grains and portlandite dissolution near the silica grains until the complete dissolution of portlandite.

Thermal mass changes of portland cement and SLAG cements after water sorption

A simple water sorption/retention (WS/WR) test, followed by stepwise static heating, was applied to the study of cement quality and the reactivity of its grain surface. The physically bound water and hence the specific surface both in the unhydrated and in the hydrated state were estimated as a function of the hydration time. Rehydration after heating at 220°C and contact with air was different inWS from that inWR samples, which indicates a difference in microstructure. XRD proved the formation of portlandite during the sorption test and eventual heating at 200°C, and its transformation into carbonates on contact with air, especially on heating at 400°C. The contents of these compounds were estimated from the mass difference between 400 and 800°C, which was compatible with the mass change between 220 and 400°C and this indicates surface reactivity. The test may serve for the routine study of cement.

Activite pouzzolanique et action de remplissage d'une fumee de silice dans les matrices de beton de haute resistance

The water reducing effect of superplasticizer in mortars is increased by addition of silica fume. The initial hydration of calcium silicates is accelerated. Consequently the formation of portlandite is increased but its quantity decreases rapidly by a pouzzolanic reaction. The improvement of the mechanical strength cannot be explained by this reaction alone. The principal effect is due to the reduction of the water-cement ratio following upon the addition of silica fume and superplasticizer.

A reply to R.L. Berger and J.F. Young's discussion of “the hydration of tricalcium silicate: Calcium concentration and portlandite formation”

A reply to R.L. Berger and J.F. Young's discussion of “the hydration of tricalcium silicate: Calcium concentration and portlandite formation”

Discussion of the paper “the hydration of tricalcium silicate: Calcium concentration and portlandite formation” by Paul A. Slegers and Paul G. Rouxhet

Discussion of the paper “the hydration of tricalcium silicate: Calcium concentration and portlandite formation” by Paul A. Slegers and Paul G. Rouxhet

The hydration of tricalcium silicate: Calcium concentration and portlandite formation

The hydration of two samples of C 3S has been studied as a function of time, with a water/cement ratio of 10. The use of a calcium sensitive membrane electrode has confirmed that the calcium concentration peak is a real supersaturation peak. However for one sample it is clear that portlandite appears before the supersaturation peak; the crystals formed at that stage show an abnormally weak 0001 X-ray reflection with respect to the 10.0 reflection.