No abstract

No abstract

Synopsis: This paper investigated the durability and hydration reaction of a 52-year-old RC structure to clarify the long-term durability of concrete using Portland blast-furnace slag (BFS) cement type C. The concrete was found to have undergone long-term strength development and to still retain calcium hydroxide and unhydrated BFS. Although it was observed that vaterite was produced and pore volume was increased by the carbonation reaction, C-S-H still remained and remarkable decomposition of hydration products, which is often seen in accelerated carbonation tests of concrete, was not observed. From these results, it is concluded that Portland blast-furnace slag cement type C can be applied to concrete structures that require long-term durability.

Hydration process of many kinds of cement paste is investigated by Powder X-ray diffraction (XRD)/Rietveld analysis. The parameters of the present study are type of cement (Ordinary Portland cement, Low heat cement, and Eco-cement), water to cement ratio (0.50, 0.35), and curing temperature (283, 293, 313K). In this contribution, reaction of aluminate phase (3CaO�Al2O3) and ferrite phase (4CaO�Al2O3�Fe2O3) is focused and evaluated. Experimental results show that the reaction of both aluminate phase and ferrite phase is affected by the temperature and presence of calcite. When system includes calcite, monocarbonate aluminate is mainly produced, rather than ettringite. And in the case of high curing temperature, Al2O3 is reacted as amorphous. Regarding ferrite phase, the reaction degree at the age of 1 year decrease as curing temperature increases, this can be presumed due to dense amorphous phase around cement minerals. Based on these experimental facts, simple hydration model is presented to evaluate development of hydration degree of aluminate phase and ferrite phase.

This study experimentally investigated how to make 300N/mm 2 ultra-high-strength concrete. The fine aggregate type was found to significantly influence compressive strength development, and the use of quartz fine aggregates yielded the highest strength. The strength of the mortar specimens made of blended cement containing silica fume reached 350-400N/mm 2 with a two-stage heat curing scheme. For concrete, the type and maximum size of coarse aggregates greatly affect the strength; the use of rhyolites up to 10mm resulted in approximately 300N/mm 2. The use of homogenous high-strength aggregates does not necessarily yield high concrete strength, likely due to the difference in Poisson's ratio.