Papers by Keyword: Cement

Abstract: Thermal conductivity is an important material property in the energy design process of the buildings. While cement-based materials are the most consumed materials in construction industry, thermal properties of these materials can play a significant role in energy efficiency of the buildings. Cementitious materials with low thermal conductivity can be desirable for using as a part of heat insulation or for thermal bridge calculations. In this study, hydrophobic aerogel granules were used as aggregate and combination of Portland cement and fly ash was considered as the binder in order to achieve a material with low thermal conductivity. Replacement of 50 vol% hardened cement paste (hcp) by aerogel granules led to about 70% reduction in thermal conductivity of air dried samples (from 0.67 W/mK to 0.20 W/mK). However, this reduction was nearly 50% in moist samples submerged in water for three days (from 0.97 W/mK to 0.50 W/mK) due to replacement of air by water in hcp pores, which can be avoided by using hydrophobic agents. The thermal conductivity can be reduced by increasing water-cement ratio as well as aerogel content. This type of composite can be used as cast concrete or on-site 3D printing of wall elements.

Abstract: The purpose of the research findings, given in article, is aimed to determine the rational compounds of concrete with an average cubic compressive strength less than 20 MPa with minimum required expenditures of cement. To reach the goal, mathematical planning of the experiment was used with variability of cement consumption from 90 to 190 kg / m³ in the compositions of the concrete mixture, and for the fine-grained filler from tails of processed ores, the consumption was like at 100 to 400 kg / m³. The result of processing experiments has shown us the dependences of the change in strength and coefficient of efficiency of the use of cement of the factors involved. Optimized values increase most intensively with minimum cement consumption and a change in the consumption of fine filler within the limits of the study. The highest coefficient of efficiency of use of cement is expressed by the ratio of the achieved strength per unit mass of used cement in the concrete mix and it was obtained at a cement consumption of 90 kg / m³ and a filler of 400 kg / m³. Using the obtained dependences of optimized values on the factors under study, the composition of concrete may be predicted with a strength up to 20 MPa with the required amount of filler.

Abstract: There are shown studies on development of the alkali-activated slag cements and concretes using Chinese raw materials. Such cements and concretes are able to provide high performance characteristics of materials and constructions under exposure of sea climate. The tests had been done for compliance with the requirements set in the national standards of P.R.China and were determined characteristics of strength, wet conditions shrinkage, freeze-thaw resistance, corrosion and weather resistance, biodegradability, water permeability, bond strength between concrete and reinforcement. The obtained positive results of tests allowed to recommend them for a pilot-scale production of the developed materials in sea construction for protection of the sea coastal line in the P.R.China.

Abstract: The paper deals with on comparison of selected properties of slag aggregate and natural aggregate in concrete. In mixtures was used as filler the slag aggregate from Koněv heap in Kladno and for comparison was used natural aggregate from Tovačov and Hrabůvka that is commonly used in concrete. The aim of this work was to verify whether this slag aggregate can be used in cement based mixtures. In the the experiment, the basic physical-mechanical parameters of both types of aggregates were determined, mixtures were proposed and then tested. Durability properties were also verified.

Abstract: Different initiatives have evolved over the years to improve the durability of concrete, and one of the promising areas gaining attention in recent years is the use of nanomaterials in concrete. Though most of the applications of nanomaterials to improve the properties of concrete has been restricted to laboratory applications, it is anticipated that in few years to come more commercial and large-scale applications will ensue. This overview explored different types of nanomaterials already used in concrete and their effects on the durability of concrete. It was found out that nanosilica is the most used nanomaterial in concrete. And all types of nanomaterials currently used, enhance the durability of concrete significantly compared to other methods employed before the advent of nanomaterials in concrete. However, the use of other nanomaterials such as nanotitania and nanoalumina is attracting great attention. But the use of nanomaterials in concrete is faced by several challenges such as its high cost, production process, toxicity, etc. It is expected that with more research and application in the use of nanomaterials to enhance the properties of concrete, cheap and user-friendly nanomaterials can be developed. In addition, this review shows the possibility of enhancing the current durability properties with the use of nanomaterials.

Abstract: The authors obtained fine grain concrete based on the mortars of additives-electrolytes undergone mechanic magnetic activation and characterized by improved compression and bending strength and enhanced freeze-thaw resistance. There was investigated the impact of mechanic magnetic activation (MMA) on mixing water when adding calcium chloride and sodium thiosulphate as well as on porosity of cement stone and specific features of phase formation in cement stone. It was stated by the authors that MMA facilitates formation of nucleation centers in activated water in the presence of additives-electrolytes, optimization of porous space as well as crystallization of calcium carbonate in the form of aragonite when lowering the content of Portlandite. The mechanism of joined influence of hydrodynamic and magnetic treatment of mixing water has been determined.

Abstract: The construction industry continues to develop and the requirements for cement performance are getting higher and higher. At the same time, in the steel industry, the discharge of steel slag is also increasing. The effective reuse of steel slag has become a prominent problem in the steel industry. . Therefore, it is envisaged to use steel slag as a raw material for the cement production process to produce cement and to produce high-performance cement. The main raw materials of this experiment are steel slag, limestone, sandstone and shale. Through the cement preparation process, the cement is made, and then the cement is made into concrete to test its performance. This experiment mainly studies the sintering temperature and holding time variable. In the experimental test, the analysis and comparison were carried out in five aspects of the degree of macroscopic cracking, particle size, density, microstructure and composition. In the comparison experiment of sintering temperature, with the increase of temperature, the flexural and compressive properties of cement gradually increased. In this test, 1200 °C is the most suitable temperature for the performance of the cement. Through the experimental comparison of different holding time, it is known that with the prolonging of the holding time, the microstructure and actual performance of the cement are continuously enhanced. Comprehensive consideration: the ratio of steel slag in cement ratio is 10%, sintering temperature is 1200 °C, and heat preservation is 2h. The steel slag cement prepared under this condition has the strongest performance.

Abstract: Garbage is a serious problem if it is not managed properly, both organic and non-organic. Inorganic waste, for example, plastic, metal, glass, and charcoal from coal combustion are difficult to decompose in the soil. HDPE (high-density polyethylene) plastic is one type of inorganic waste that is difficult to decompose, but this plastic can be recycled. The objective of the study is to develop light cement blocks by using the waste of HDPE, coal bottom ash and cement. The research guide was referred to SNI (Indonesian National Standard). The SNI-03-6825-2002 is for testing of the compressive strength and SNI 03-0349-1989 for the testing of the water absorption. The size of the specimen was 5 x 5 x 5 cm. In this study, the compositions of HDPE: coal bottom ash were varied by 70%: 0%, 60%: 10%, 50%: 20%, and 40%: 30%. The Holcim cement was 30% of the volume fraction. Testing was conducted after the specimens stay in 7 and 28 days. For the 7 days old of specimens, the highest compressive strength has resulted from 50%:20% composition with the value of 5.88 N/mm2. For the 28 days old specimens, the highest compressive strength was 8.34 N/mm2. The lowest water absorption test was delivered by the more coal bottom ash in the composition of 40%:30%. It was 16.971%. The more coal bottom ash, the less water absorption. The mean of specimens density was 1.076 gr/cm3. The result of the research shows that recycles HDPE and coal bottom ash as concrete block meet the required strength.

Abstract: This paper studies the fundamental research and development of sprayed cement-based mixture designed to withstand the chemically aggressive conditions. The aim of this paper is to verify the possibilities of usage of suitable secondary raw materials as a substitution of a binder and filler of the original mixture while preserving or improving the physical-mechanical properties. In this part of the research was studied the possibility to substitute the binder in rate of 20-60 wt.% by high temperature fly ash and the whole filler by foundry sand and slag. Test samples were made from nine recipes, in which was monitored the influence of secondary raw materials on the compressive strength and the water absorption after 28 days of curing. The results of this paper show, it is possible to successfully substitute part of the binder by high temperature fly ash and the filler wholly by foundry sand in the sprayed mixture. These optimized recipes showed positive influence mainly in the long-term on mechanical properties.

Abstract: Studies have revealed that wood ash cement concrete just like other pozzolanic cement concrete has lower early strength compared to plain cement concrete. Nanoparticles have been found to improve the early strength of concrete due to its small size and large surface area. This paper reports the findings on influence of nanosilica on the workability and compressive strength of wood ash cement concrete. Wood ash was obtained as a waste product from Ladoke Akintola University of Technology (LAUTECH) bread bakery, Ogbomoso. Biological synthesis of nanosilica using kola pod extract and silica precursor (1:5) was conducted at Nanotechnology research group laboratory at LAUTECH. The chemical composition, specific gravity and grading of wood ash, fine and coarse aggregate used were determined. Concrete with 10% wood ash replacement for cement was produced using 1:2:4 mix proportion and water to binder ratio of 0.5. Nanosilica was added at 0.5, 1.0, 1.5 and 2.0% levels. Concrete with no wood ash and nanosilica served as the control. Workability and compressive strength of the plain and composite concrete were determined. The results showed that concrete workability was enhanced with introduction of nanosilica. The compressive strength also increased with the addition of nanosilica. Maximum compressive strength of 27.53MPa was achieved at 90 days with 1.5% nanosilica addition. It was concluded that nanosilica enhanced workability and improved both early and later strength development in wood ash concrete with 1.5% as the optimum addition.