International Concrete Abstracts Portal

A new environment-friendly block, called "steel slag hydrated matrix", consisting mainly of steelmaking slag, ground granulated blast furnace slag, fly ash, and water was developed. Steel slag hydrated matrix has the following features: 1) Made from 100% recycled resources, 2) same strength performance as ordinary concrete, 3) excel-lent wear resistance, 4) low alkaline dissolution, and 5) excellent growth habitat for biofouling organisms in marine environments. In repair work at Mizushima Port, Okayama Prefecture, Japan, 150,000 tons of steel slag hydrated matrix material were used. The ease of use in construction and low impact on ecological systems of the new material were confirmed in the course of this work.

Chloride ingress into concrete is commonly modeled using Fick's second law of diffusion. The common form of Fick's second law was derived for the boundary condition of one surface being in contact with a reservoir of constant concentration, such as the submerged portion of a marine seawall. However, in structures exposed to cyclic wetting and drying, this constant concentration boundary condition is not satisfied. Essentially, in cyclic exposures the surface concentration is not constant, but increases as a function of time. Chloride ingress occurs through sorption and diffusion in such exposures, but solely through diffusion in saturated environments. This paper compares the difference between chloride ingress in concrete exposed to cyclic wetting and drying environments with that of submerged concrete. This multi-year evaluation consisted of six different concrete mixtures, five of which contained different supplementary cementing materials. In addition, each concrete mixture was tested with and without a surface applied silane sealer. The results of these evaluations illustrate the relative rates of chloride ingress in the different environments and the effectiveness of supplementary cementing materials when combined with a silane sealer to reduce chloride ingress in cyclic exposures.

The paper shows the influence of mineral additions (in form of fly ash, slag and ground limestone) replacing portland cement on the COz penetration rate of concretes manufactured at a given water-cementitious material ratio (w/cm). The results indicate that at a given w/cm there is an increase in the carbonation rate in concretes with mineral additions, except when the amount of portland cement replacement is relatively low (15%). On the other hand, when the comparison of the carbonation rate is made on concretes at the same strength level, there is no significant difference between concretes with portland cement and those with replacement by mineral addition up to 50%.

The influence of silica fume (SF) on the plastic viscosity, yield point and gel strength of cementitious paste has been studied. A super-plasticizer based on polyacrylate with grafted polyether chains (SSP) was used. The effect of delayed addition of super-plasticizer versus addition with the mix water was investigated as well as the effect of densified versus untreated silica fume. Inert limestone slurries with SF replacement were used as comparison. The results showed that there was not much to gain in terms of lower shear stress in flow curves by delayed addition of this particular SSP. The plastic viscosity had a de-creasing tendency with increasing SF replacement, while yield stress was rather constant. Plastic viscosity increased with increasing time. There was a substantial increase in 10 min gel strength with increasing SF replacement. Gel strength was lower for mixes with densified SF versus untreated SF. Delayed SSP addition reduced gel strength for cementitious pastes with 10% SF. Neutral limestone pastes with increased SF replacement had increasing gel strength from 6 vol% replacement. Densified silica fume gave 10 times less gel strength than untreated SF. Increasing pH from 8 to 13.2 in limestone slurries with 10 vol% SF increased the shear stresses substantially.

Large quantities of municipal solid waste combustion residues are produced during the incineration of municipal wastes. The necessity of utilizing (MSWI) fly ash for manufacturing ecological and energy saving cements was the aim of this investigation. A partial substitution of Portland cement clinker by MSWI fly ash and zeolite which is a common raw material in Ukraine has led to manufacture high-quality blended cements. Three mineral additives were mixed in the clinker. The systems consist of 50 to 800/c clinker, 10 to 30% blast furnace slag (BFS), 10 to 20% zeolite, and 10 to 20% MSWI fly ash, and 5% gypsum added for all systems. The study evaluated compressive strength of pastes made with these binders, along with the effects of binder proportions. The changes in strength were monitored by differential thermal analysis (DTA) and scanning electron microscope (SEM). Three endothermic peaks appear at 150°C, 400°C, 780°C due to the loss of water, modification of morphology, and carbonates decomposition. SEM was used to study the morphology of hydrating binders. Needle shape and fibre crystals of calcium hydrosilicate and tabular hexagonal plates of Ca(OH)2 were noticed. CaCO3, quartz, hydrocarboaluminates, and calcium hydrosulfoaluminates were also present. XRD patterns show that zeolite play an important part. Its presence leads to an activation of the hydration process and an acceleration of pozzolanic reaction between Ca(OH)2 and cement additives. The 5001c clinker, 30% BFS, 10010 MSWI fly ash, 10% zeolite cement system was the optimum quantity of MSWI fly ash which could be re-cycled in the manufacture of ecological and energy saving cement of high-quality.