International Concrete Abstracts Portal

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.

The rheological properties, the packing density, and the final matrix strength of high performance cementitious materials can all be improved by adding fine-grain materials such as fly ash, silica fume, slag, and natural pozzolans. Beside size and shape of the added materials, their pozzolanic activity can improve the bond between the particles in the matrix and can reduce the shrinkage. In this study, the fine-grain binder systems were evaluated for application in high performance fiber reinforced cementitious composites with different type of non metallic fibers (carbon, PVA, PP). The rheological and mechanical properties of fiber reinforced composites based on ordinary portland cement and blended with micro-fine cement (mostly based on blast furnace slag), fly ash, silica fume, and limestone filler, respectively, were measured and compared to the pure fiber-cement matrix. In this context, micro-fine cement shows clear advantages compared to the other fillers. Very good mechanical properties of the composites (flexural strength > 25 MPa, compressive strength > 150 MPa) were obtained. For the estimation of the consistency of fiber-cement mixtures, a new experimental method was developed and applied.

The objective of this research is to study the compressive strength of mortar due to pozzolanic reaction of fly ash with different particle sizes. Fly ash and river sand which were ground to have median particle sizes of 19.4, 13.8, 6.3 pm and 20.6, 11.7, 6.4 µm, were used to replace portland cement type I at the rate of 10, 20, 30, and 40% by weight of cementitious materials to cast mortar. The pozzolanic reaction, without packing effect, of fly ash mortar is obtained from the difference of compressive strength between ground fly ash mortar and ground river sand mortar which have approximately the same particle size (19.4 and 20.6 pm, 13.8 and 11.7 µm, 6.3 and 6.4 µm) and the same replacement. The results showed that the pozzolanic reaction of fly ash mortar in-creases with the increase of fly ash fineness, age of mortar, and percent replacement of fly ash. Ground fly ash with particle sizes between 6.3 to 19.4 µm have slight packing effect on compressive strength of mortar. At early ages, the contribution to compressive strength of fly ash mortar due to pozzolanic reaction is slight, but it significantly in-creases at later ages. With 40% replacement of 6.3 pm particle size of fly ash, the compressive strength of mortar due to pozzolanic reaction at the age of 90-day is more than 50% of the total compressive strength of mortar.