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Properties Of Concrete

This study presents the effect of incorporating metakaolin (MK) on the mechanical and durability properties of high strength concrete for a constant water/binder ratio of 0.3. MK mixtures with cement replacement of 5, 10 and 15 % were designed for target strength and slump of 90 MPa and 100 ± 25 mm. From the results, it was observed that 10 % replacement level was the optimum level in terms of compressive strength. Beyond 10 % replacement levels, the strength was decreased but remained higher than the control mixture. Compressive strength of 106 MPa was achieved at 10 % replacement. Splitting tensile strength and elastic modulus values have also followed the same trend. In durability tests MK concretes have exhibited high resistance compared to control and the resistance increases as the MK percentage increases. This investigation has shown that the local MK has the potential to produce high strength and high performance concretes.

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Effect of Metakaolin Content on the Properties of High Strength Concrete

THE STRENGTH OF CONCRETE MADE FROM SOUND, DURABLE MATERIALS DEPENDS UPON THE EXTENT TO WHICH THE SOLID PARTICLES ARE BONDED TOGETHER AND THE AMOUNT OF SOLID MATERIALS IN THE CONCRETE. THE BOND DEPENDS UPON THE PROPORTION OF CEMENT IN A GIVEN QUANTITY OF CONCRETE AND THE AMOUNT OF MIXING WATER. USING THESE BASIC PRINCIPLES SEVERAL METHODS FOR DESIGN ARE AVAILABLE. IN ANY CASE, THE MAINTENANCE OF A CONSTANT RATIO OF CEMENT TO MIXING WATER IS ESSENTIAL TO UNIFORMITY OF RESULTS. THE NEED FOR ACCURATE MEASUREMENT OF ALL MATERIALS IS EMPHASIZED AND ADEQUATE METHODS ARE DESCRIBED. AN EXAMPLE OF THE USE OF THE MORTAR-VOID METHOD OF DESIGNING TO MEET AN UNUSUAL CONDITION IS INCLUDED.

Design of concrete mixtures

The primary goal of concrete mixture design is to strike a balance among workability, compressive strength, durability, economic efficiency and sustainability. In this paper, for a given strength grade, the optimum paste consisting of cement, fly ash and slag, and the optimum ratio among paste, fine aggregate and coarse aggregate were optimized using the simplex centroid design method based on rheological properties. Results showed that the optimum content of total cementitious materials in concrete could be obtained according to the relationships between the workability, yield stress, plastic viscosity and the paste volume fraction. The optimum replacement of supplementary cementitious materials could be determined according to the rheological properties and compressive strength of concrete with ternary cementitious components. It is an effective way to optimize the mixture design of concrete based on the rheological properties using the simplex centroid design method.

Mixture design of concrete using simplex centroid design method

Determination of steel fibres distribution in self-compacting concrete beams using X-ray computed tomography

Metakaolin forms a part of a complex admixture to self-compacting high-strength concrete. The admix34 ture contains superplasticizer addition of naphthalene formaldehyde or polycarboxylate type, yielding

2 Using mathematical modeling for design of self compacting high strength concrete

The article is devoted to the study of the effect of lime kiln dust (LKD) on the properties of concrete mixtures and concrete using Portland cement and fly ash. A possible mechanism for the formation of the structure of cement–ash paste with the addition of LKD is analyzed in detail. The positive effect of LKD on hydration (an increase in the content of hydration water by 40.50%) and structure formation due to an increase in the alkalinity of the cement–ash paste is shown. Using the method of the experiment mathematical planning, experimental–statistical polynomial models of the concrete component (Portland cement, fly ash, dust, superplasticizer, and aggregates) content influence on the workability of the concrete mixture and the strength of concrete at different ages were obtained. The introduction of lime–carbonate components into concrete mixtures increases the strength of concrete by 27%–54%. At the same time, with the consumption of cement up to 200 kg/m3, ash 100.150 kg/m3, and LKD 50.100 kg/m3, it seems possible to obtain concrete with a compressive strength of 20.30 MPa. The obtained models were analyzed, which made it possible to establish the positive effect of LKD additive on the compressive strength of concrete at the age of 7–180 days.

Cement–ash concrete with the addition of lime kiln dust

An experimental investigation was conducted in order to study the water absorption, mechanical performance, thermal properties and durability of hybrid hemp-rapeseed composite materials. The hybrid composite material is made with 50% hemp shives and 50% rapeseed fibres. The purpose of this study is to investigate the influence of the incorporation of viscosity modifying agent (VMA) on hybrid concrete. Four mixes were made for: shuttered walls and roof insulation with and without VMA. The water absorption of the hybrid composite fibres was, first, measured. The compressive strengths of these mixes at 7 and 28 d were then determined in order to compare the mechanical behaviour of the hybrid composite materials made with VMA. In addition, the capillary absorption and coefficient of thermal conductivity were also measured. The results revealed that VMA improved the performance of the hybrid concrete.

Effect of Viscosity Modifying Agent on the Performance of Hybrid Bio-Based Concrete

The article is devoted to the issues of obtaining pressed building materials based on dihydrate phosphogypsum. Dihydrate phosphogypsum after mechanical activation in a ball mill acquires the ability to harden in pressed specimens. After activation of dihydrate phosphogypsum in a ball mill and its pressing at a pressure of 30 MPa, the strength of specimens increases by 6...8 times compared to non-activated specimens and reaches 25...30 MPa. There is found the influence of various chemical admixtures on binding properties of activated phosphogypsum and there are shown possibilities of water resistance improvement and increasing of other properties characterizing this material. There is studied an effect of aggregates on the building and technical properties of artificial stone made of phosphogypsum and peculiarities of its structure and change under the influence of different factors.

Binders for pressed products based on phosphogypsum waste

The article presents the methodology of designing the composition of fine-grained concrete, taking into account the method of compaction, the parameters of the aggregate and the binder obtained on the basis of a complex of experimental studies. The results of studies of the effect of the type of concrete mixtures and their method of compaction on the strength of fine-grained concrete and the relationship of strength with water-cement ratio are presented. An original method of determining the thickness of a cement paste film on aggregate grains is proposed, which allows one to calculate the ratio between the components of a concrete mix based on the physical model of the concrete structure. The developed calculation methodology can be used both on computer systems and manually thanks to the built nomograms. This methodology is suitable for practical application in determining the composition of concretes for fine-walled and thin-walled products, as well as for thick-reinforced, reactive-powder concretes and fiber concrete.

Leonid Dvorkin

Papers

2 Using mathematical modeling for design of self compacting high strength concrete

Cement–ash concrete with the addition of lime kiln dust

Effect of Viscosity Modifying Agent on the Performance of Hybrid Bio-Based Concrete

Binders for pressed products based on phosphogypsum waste

Methodology for Calculating the Composition of Fine-Grained Concrete with High Resolution