International Concrete Abstracts Portal

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.

Alkali activation of fly ashes is a chemical process through which the glassy structure of the material is transformed into a very well compacted cement. In general terms a variety of natural materials and industrial by-products rich in S'02 and Al2O3 may be activated with certain alkaline compounds to produce cementitious systems when cured under mild temperature conditions. The activation process may be considered as a set of destruction-condensation re-actions that initially lead to a series of unstable structure units and later produces the formation of tixotropic coagulation structures, which can condense to form the hydrated products. This paper describes a micro-structural study of a number of alkali activated fly ash matrices. MAS-NMR results has shown that the main reaction product in the activation of fly ashes is an amorphous aluminosilicate gel having a 3-dimensional structure in which the Si evolves in a variety of environments with a predominance of Q4(3Al) units when curing time is short, and Q4(2Al) units when curing time is long. Aluminium is essentially tetrahedrally co-ordinated. Microanalysis has provided additional information on the Si/AI ratio of the mentioned aluminosilicate gels too.

High fluidity concrete needs appropriate amount of powder for preventing concrete segregation. But slump flow often decreases because of the properties of powder. It is important to investigate qualities of the powder influencing rheological properties of concrete. So, the purpose of this study is to investigate an evaluation index for segregation resistance and the qualities of powder relating to the index. Firstly, the evaluation indices for segregation resistance were examined. And the best proposed as the ratio between coarse aggregate weight in concrete contained in the lower part of cylindrical vessel and that in upper part after tamping by a steel rod. This index more accurately ex-pressed the segregation potential under construction. Plastic viscosity of mortar and volumetric percentage of coarse aggregate in concrete mainly influence the index. Next, we investigated the influence of fly ash, Blast-furnace slag powder, limestone powder, crushed stone powder and recycled concrete powder on properties of a mortar. If the surface of powder was rough, the mortar flow with the powder largely decreased with in-creasing plastic viscosity when quantity of the powder was increased.