SCC modification by use of amorphous nano-silica

In this study two different types of nano-silica (nS) were applied in self-compacting concrete (SCC), both having similar particle size distributions (PSD), but produced through two different processes: fumed powder silica and precipitated silica in colloidal suspension. The influence of nano-silica on SCC was investigated with respect to the properties of concrete in fresh (workability) and hardened state (mechanical properties and durability). Additionally, the densification of the microstructure of the hardened concrete was verified by SEM and EDS analyses. The obtained results demonstrate that nano-silica efficiently used in SCC can improve its mechanical properties and durability. Considering the reactivity of the two applied nano-silicas, the colloidal type showed a higher reactivity at early age, which influenced the final SCC properties

Influence of combined carbonation and chloride ingress regimes on rate of ingress and redistribution of chlorides in concretes

In majority of exposure environments for concrete structures, there is a high probability of the cyclic occurance of both chloride ingress and carbonation. This paper reports a detailed investigation on the influence of carbonation on both the ingress and distribution of chlorides in three different types of concretes, by comparing results from exposure to chlorides, chlorides before carbonation and chlorides after carbonation. Concretes studied were of 0.55 water-binder ratio with 100% Portland Cement (PC), 70% PC + 30% pulverized fuel ash (PFA) and 85% PC + 10% PFA + 5% microsilica (MS) as binders. Chloride profiles were compared to assess the effects of all variables studied in this research. The effect of carbonation was quantified by measuring the consumption of hydroxyl ions (OH-), air permeability and chloride migration coefficient. The results indicated that carbonation of concrete increases chloride transport, but the precise nature of this is dependent on the combined regime as well as the type of binder. In general, it was found that carbonation of chloride contaminated concretes results in a decrease of their chloride binding capacity, that is it releases the bound Cl- in concretes and pushes chlorides inwards, as has been established previously by other researchers. However, it is established in this research that the combined regimes detrimentally affect the service life of concrete structures, particularly when chloride induced corrosion is a concern