International Concrete Abstracts Portal

Alkali-activated slag concretes (AASC) are relatively well-known composites. For practical application various different problems must be solved. For example, they are the optimum content of alkaline activator and its nature; the composition of the activator for optimum setting and hardening time; the design of concrete for good workability, for the reaching of the smallest volume exchanges, and for maximum strength and for high durability. These problems are discussed in the present paper. Water glass and/or natrium hydroxide were chosen as the best type of activator and the optimum ratio Na2O and SiO2 were found. Calorimetry, MAS NMR (27Al and 29Si), SEM and other methods were used for the characterisation of the mixes. The concrete mixes are designed as self compacting for easier introduction of these materials into practice. Strengths, volume changes and their time development were measured during the aging of the mixes. Some elements will be produced from the concretes in 2005 and 2006 (elements for cable pipe-lines).

This research evaluated, from the ecological and economical points of view, the potential use of high volumes of incineration ash from sewage sludge in CLSM (Controlled Low Strength Materials). Moreover, a dust powder from crushed stone production is used as a fine aggregate. This new type of green CLSM will be a promising sustainable cementitious material for reducing CO2 emissions. In-situ early-age strength estimation of CLSM was proposed with applying simple cone penetration method (so-called YCP Test, Yamanaka Cone Penetration Test), which has been used for soil strength estimation. Test result showed that the YCP Test is found to be effective for estimating the in-situ early-age compressive strength of CLSM. Test results also showed the adequate strength development and reasonable flowability are confirmed if the mixture proportion is carefully selected. Although, the compressive strength decreases with increasing level of incineration ash, this strength reduction is easily compensated for increasing a small amount of cement content. From these tests results it is confirmed that a wide range of municipal solid waste is applicable for the materials of a new green CLSM.

This paper describes the effect of fly ash on composition of C-S-H gel. The CaO/SiO2 ratio and chemical bonding water of C-S-H gel were estimated by the combination of the Rietveld analysis by XRD, the selective dissolution analysis and loss of ignition measurement. The results indicated that the CaO/SiO2 ratio of hydrate gel in fly ash-portland cement paste decreased as the hydration of fly ash proceeds, while the CaO/SiO2 ratio of C-S-H gel in portland cement paste did not vary with the progress of hydration. At the same amount of produced C-S-H gel, bonding water in C-S-H gel of paste prepared with 50% fly ash was higher than those of pastes prepared with of fly ash 25% and 0%. The corresponded results can be seen from decreasing of density of C-S-H gel when replacement ratio of fly ash increases. The bonding water in C-S-H gel decreases as its CaO/SiO2 ratio increases. The effect of chemical bonding water in C-S-H gel can be applied to modify the gel/space-strength model.

In this paper experimental evaluation on the effect of high volume fly ash as partial replacement of cement on fracture toughness of cement mortar are presented. The fly ash replacement level was 50%, 60% and 70% by weight of cement. Three-point bend notch beams were used to measure the fracture toughness of mortar. Results show that the use of 50% fly ash as partial replacement of cement reduces the fracture toughness values between 38% and 58% compared to that without fly ash. Reduction of compressive strength and Young’s modulus in mortar containing 50% fly ash as partial replacement of cement compared to that without fly ash is also observed in this study. The use of 60% and 70% fly ash as partial replacement of cement is found to have negligible effect on the reduction of fracture toughness of cement mortar. Long term effects of high volume fly ash (50% cement replacement) on fracture toughness, compressive strength and Young’s modulus of cement mortar are also evaluated in this study. Tests were conducted at 28, 56 and 91 days and at 5, 7, 10 and 12 months. Results show that the rate of increase of fracture toughness of cement mortar containing 50% fly ash with time is very slow. Compressive strength and Young’s modulus also increase with time.

Finely ground lightweight aggregate (LWA) based on calcined and expanded clay has been proven to be quite an effective pozzolan. When replacing cement with 15% LWA fines the concrete compressive strength becomes more sensitive to temperature and time, and 28 day strength is typically 10-15% lower when cured at 5 °C, equal when cured at 20 °C and 15% higher when cured at 35 °C. However, cement replacement by such a mineral increases the concrete resistance to chloride ingress, reduces alkali aggregate reactions and increases the sulfate resistance. Carbonation rate, on the other hand, is somewhat increased as for most pozzolana. Freezing and thawing resistant concrete can also be made with this additive. Thus, finely ground LWA can be utilized to make high performance concrete.