Cement, Energy and Environment

On the X-axis then, the C-S-H forms the bulk of the points. Many of the points fall in the region of 0.5 along the axis, providing the ratio of 2:1 ratio Ca to Si in the C-S-H. These relatively pure compositions will be those collected from the C-S– H formed in situ as the C 3 S or C 2 S grains were hydrated . It is apparent that even the pure C– S-H does not lie directly on the X-axis, but slightly into the field represented by a raised AI/Ca ratio. In other worlds, in Portland cement paste, aluminium forms an rntegral part of the C-S-H composition. For the analyses collected from the original water-filled space tne C– S-H is less pure and contains some CH and some AFm as can be seen from the extension of the plotted group along lines towards those composition? as plotted on the chart. Because this is a mature cement paste, the extension into the AI rich part of the chart is towards AFm, the monosulphate and not towards AFt. ettringite. Increased cement strength For a cement maker, in practice, some benefit can be gained from a knowledge of the hydrated chemistry of the cement paste in manufacturing cement clinker which will b~st serve tne customers' needs. There is a general awarene~s that c3s is an important constituent in cement and a . . ' ~ \ 1 ·- I .. ----- --- ' .. L : : I .. ---- 0 .. 1 .. t .. I < J.. i .. •• • .... •• •• ... . .. ,,. '---...,.,......, .. ._ )·*~~~~--~~----~+* flO-~ ... general view that the higher the C 3 S content, the stronger will be the cement. While this view contains some truth, filling a cement clinker full of C 3 S at the expense of harder burning and harder grinding does not keep producing stronger cement. The relationship shown in Figure 4 demonstrates that once the optimum has passed. further increasing the LSF of a clinker and therefore the proportion of the clinke r which is c3s. achieves no improvement and eventually leads to a decrease in performance. For the vast majority oi applications the means of increasing strength wrth Portland cement is nm in providrng a stronger glue to hold the aggregate grains together. In practice , the bond between aggregate and cement plants is very weak. The first aim is to fill in as much of the space between the aggregate grains and also between the cement grains, as possible. This achieved firstly by making the spaces as small as possible. When making concrete water in the mix is equal to space to be filled (air-filled space will not be filled by useful reaction products), therefore the less water is used , the stronger will be the concrete. The mix must, however, be workable as discussed last time. For most applications a dry mix is undesirable, the air filled space will reduce strength . What is important is to match the amount of cement hydrate produced to the amount of space required to be filled. Another means of filling water-filled space faster is to mal<e the cement grains themselves fi ner. The solubility of all the species forming the bulk of the cement paste is low and it is important to allow them to be dissolved, pass through