Cement Energy and Environment

"-. A crude measure of the density of the hydration products is the ratio of IW to the sum of IW and the gel pore water. The evolution of this ratio during hydration can be compared between treatments by plotting against IW% as a measure of hydration degree (Fig. 8). Following the induction period and ITO where initial capillary water was transformed to IW without gel pore formation , the ratio declined during the gel pore formation and reached a very similar minimum value for all treatments at the end point of this period. The degree of hydration at which this minimum ratio occurred was also similar, although there was the appearance of a small effect of greater retardation resulting in the minimum occurring at a lower IW%. This effect, while possibly random in nature, might suggest that a denser microstructure could eventuate later during hydration under greater retardation. Nevertheless, all treatments appeared to converge and track an identical path following the start C-S-H densification (Fig. 8). the rates of IW and gel pore formation are expected to be generally correlated during this period. However, the behaviour illustrated in the plots indicate that the relationship is not constant and that a small increase in hydration rate, relative to the overall trend , is accompanied by a marked increase in the rate of gel pore formation. In the no retardant case (Fig. 7A), the peak at -21 h is associated with a shoulder region on the deceleration side of the main hydration peak, and the more complex prominent double at peak at -35 h is associated with the secondary hydration peak. The association with a secondary peak is very prominent at 50 h in the high citrate treatment. Clearly, during these peak periods, the rate at which capillary water is being converted to gel pore water increases substantially compared to the rate of incorporation into hydration products. The following possibilities are suggested by these patterns of behaviour. 1. Changes in structure and density of the of C– S-H product may be occurring due to interactions with new phases, such as sulfoaluminates, that impact growth and/or packing of C- S- H. 2. Measured gel pore water may be a net amount resulting from a dynamic process where gel pore water is continually consumed at the same time as capi llary pores are transformed to new gel pores via the production of hydrates. The sudden switch to gel pore water consumption at the end of the gel pore An intriguing feature can be seen in the plots of changes in water content of capillary and gel pores where the apparent amplification of features in the total water plots occurs (Fig. 7). This is particularly the case in the no retardant treatment at - 21 h and -35 h and in the 2 g kg-1 citrate treatment at -50 h. The early hydration process, at least until gel pore production ceases, involves the transformation of capillary pores to either 1) hydration products (IW) or 2) gel pore water within the interstices of these hydration products. Hence formation period, at least for the two M.W. 8/iglr eca/.f('rmrru and Corj least retarded treatments (Figs. 6 ,------- 138 .-----------------.. and 7), suggests that this could be ~ 0.9 a. (!) 0.8 + ~ 0.7 ~ 0.6 10 No Retardant Citrate 1.3 g.kg 1 Citrate 2 g.kg 1 Retarder N 10 mlkg · 1 20 30 40 50 IW(%) 60 Fig. 8. Ratio of incorporated water (IW) to the sum of IW plusgel pore water (Gl'W ), I which together constitute thewater associated with hydr.!tlon products, as function ~of thedesr-ee of hydradon expressed In terms of IM . Until the start of gel pore for11ldtlon. capillary water is transformed only to IW, then during gel pore formation lhe ratio declines and reaches a minimum when formation ceases and c S- H densr/lcation L commences. --- ---- the case. As such, the net process becomes negative when gel pore formation ceases while hydration continues. During the above periods of interest, the balance between capillary and gel pore water consumption may change, producing the effect of an increased rate of gel pore production. Conclusions The key conclusions resulting from this study are as follows. 1. The high correl ation between the rate of incorporated water (IW) production and the rate of heat 63