Papers by Keyword: Setting Time

Abstract: The paper presents the results of studies of the effect of the concentration of binder components on the properties of cement alkaline stone. Formulations of clinker-free binders of alkaline activation with the level of filling the system of 20 and 40% have been developed, the properties of the cement paste of the binding binder "aspiration dust - mineral powder - liquid glass" have been studied, the dynamics of a set of strength indicators has been studied, both for bending and compressive forces. The received results allow to estimate uniqueness of properties of a binding binder "a mineral powder - Na₂SiO₃" and to create new materials on resource saving and energy saving technology. The results presented in this article were obtained within the framework of studies on the implementation of scientific project No. 05. 607.21.0320. "Development of technology for new building composites based on clinkerless cement of alkaline activation using substandard natural and secondary raw materials" supported by the Federal Target Program "Research and Development in Priority Areas of Development of the Scientific and Technological Complex of Russia for 2014-2020". The unique identifier for the agreement is RFMTFI60719X0320.

Abstract: Silicate micro- and nano-additives are multifunctional in relation to cement systems. Their application can solve a wide range of technological problems while maintaining the economic efficiency of technical solutions. The effect of silicate additives and fillers is determined by their level of dispersion, due to which the technologies for producing nano- and submicro-sized dispersed materials are being developed. The combination of mechanochemical synthesis of modified calcium hydrosilicates with subsequent thermolysis makes it possible to produce calcium silicate dispersions (SCD), which differ in polymodality of the fractional composition including submicro (10^–7–10^–6 m) and microdimensional (≥10^–6 m) modes. The main element of the technology is the use of modifying carbohydrate, which acts as a stabilizer of hydrated phases of silicates. A comparative study of SCD produced using sucrose (sSCD) and lactose (lSCD) revealed the effect of these carbohydrates on the properties of sSCD and lSCD, as well as their effectiveness as a component of cementitious composite binder. It was found that the level of adsorption of modifying carbohydrate determines the physical properties of SCD (granulometry, specific surface area). The relatively high residual content of free sucrose (0.24%) in the composition of sSCD prevents the consolidation of silicates nanoparticles formed during the thermolysis, causes a high content of submicro sized fractions and a high specific surface area with sSCD (26.3 ± 0.7 m²/g). Lactose is absorbed by the silicate phase; the residual content of free lactose does not exceed 0.028% of lSCD. The low content of stabilizing carbohydrate contributes to the development of nanoparticle consolidation, a decrease in the specific surface area of lSCD to 13.0 ± 0.2 m²/g and content of submicrosized fractions. The residual content of free carbohydrates and particle size characteristics of sSCD and lSCD determine the nature of their influence on Cement-SCD-based concrete setting and hardening. The presence of residual sucrose in the composition of sSCD and fine fractions determines the competitive nature of the processes of retardation of hardening and acceleration of hardening of the cement system due to the nucleation effect, as a result of which the curve of the setting time is extreme. In addition, the inhibitory effect of sucrose reduces the strength of concrete on the 7^th day. By the 28^th day, the inhibitory effect of sucrose has been overcome, and concrete samples demonstrate an 18% increase in compressive strength with a sSCD content of 30%. The low content of residual free lactose in the composition of lSCD causes the nucleation effect. As a result, there is a monotonous reduction in the setting time of concrete mix with an increase in the content of lSCD in the composition of HF, as well as a significant increase in concrete strength (up to 127%) on the 7^th day. At the same time, on the 28th day the strength of concrete increases slightly

Abstract: A highly porous structure of a gypsum product creation is possible due to the porisation of gypsum mass, using new types of complex gas-forming components. At the same time, it is necessary to determine the technological conditions for the optimal formation of porous gypsum products structure and methods for increasing their strength. The article proposed to use dispersed calcium carbonate and aluminum sulphate, which interaction is the reaction with the release of СО₂ for the porisation of the gypsum cast mixture. Micro-reinforcing additives, such as polymeric, basalt and glass fibers were introduced into gypsum composition together with building gypsum and finely ground calcium carbonate to improve the physico-mechanical properties of gas-gypsum. The best results were shown by the gas-gypsum, which included fiberglass. Glass fiber was pre-ground to a specific surface of 190-240 m² / kg, in order to improve further the physico-mechanical properties of gas-gypsum.

Abstract: Apatite cement is ideal self-setting cement for bone substitute material, however its use is limited only to areas that receive minimum load bearing because mechanical strength of apatite cement is low. Silica-calcium phosphate nanocomposite (SCPC50) is material having good mechanical strength and has an important role in bone remodeling (bone metabolism), mineralization, synthesis of cartilage, collagen production, proliferation and differentiation of bone cells. However, the unsetting and granule’s physical shape of SCPC50 limits the application. The purpose of this study is to determine the effect of various mixtures of SCPC50 and apatite cement to manipulative index (setting time and handling property), and mechanical properties. The experimental results show that the setting time of apatite cement mixture with 5% and 10% SCPC50 was 40% higher (p<0.05). The mechanical strength evaluated by Diametral Tensile Strength showed that the addition of both 5% silica and 10% SCPC50 composition to apatite cement mixture increased the mechanical strength of apatite cement mixture (p<0.1). The handling property of cement paste was significantly increased between the apatite cement without SCPC50 and apatite cement with both 5% SCPC50 and 10% SCPC50 (p<0.05). It is concluded that the addition of SCPC50 to apatite cement mixture could improve the mechanical properties and it is expected to improve its bioactivity.

Abstract: The peculiarity of alkali-activated slag cements (further, AASC’s) is increased proper deformations, which can cause increased cracking and reduced durability of structure. The paper is devoted to manage AASC’s proper deformations. The main task was to determine the composition of complex additives (further, CA’s) in system «ordinary portland cement (further, OPC) clinker - mineral compound of different anionic type - surfactant» in presence of sodium metasilicate (further, MS) to affect on hydrated AASC performance while ensuring effective structure of artificial stone by criterion of shrinkage deformations. Comparative analysis of hydrated cement systems "OPC clinker - MS", "OPC clinker - mineral compound - MS" and "OPC clinker - mineral compound - MS - surfactant" showed that the greatest effect on reduction of proper deformations occurs when the mineral compounds relate to electrolytes, i.e. Na₂SO₄ and NaNO₃. Hydrated system is characterized by expansion (+0,062 mm/m) in presence of Na₂SO₄. Almost no shrinkage is supplied by application of NaNO₃ (-0,062 mm/m). The obtained CA’s were tested in AASC. CA in the system “OPC clinker - NaNO₃ - surfactant” provides the initial setting 43 min, the end - 65 min with accelerated strength. Investigated AASC can be classified as non-shrinking cement. This phenomena is ensured by increasing density, homogeneity and monolithicity of hydrosilicate formations, as well as due to formation of hydroaluminosilicate structures with different morphology by inclusion of nitrate anions.

Abstract: This paper examines and present the findings of the physical and mechanical properties of concrete containing rice husk ash (RHA), and the blend of rice husk ash with calcium carbide waste (RHA-CCW). Concrete cubes, cylindrical and beam specimens containing different percentages of RHA and RHA-CCW by weight of cement (5, 10, 15 and 20 %) were cast. Compressive strength test was carried out after the specimens were cured in water for 7, 14, 28 and 56 days. Test for tensile and flexural strength was carried out after 28 days curing. Initial and final setting time test was carried out on mortar specimens with the same percentage of RHA and RHA-CCW. Bogues model was used to determine the elemental and compound composition of cement when blended with the RHA and RHA-CCW. From the results obtained, the compressive strength of RHA-CCW concrete increases as cement is partially replaced with RHA-CCW content, with the maximum strength attained at 5 % replacement. RHA concrete attains it maximum strength at 10 % replacement. The maximum compressive strength results obtained for both RHA and RHA-CCW concrete were higher than the strength of plain concrete (0 % replacement) by 1.1 % and 14.7 % respectively. Interestingly, results obtained for the tensile strength also shows a similar pattern of strength development with that of compressive strength. The flexural strength properties of concrete was improved upon when RHA-CCW was used in concrete compared to RHA. The results of setting time test for RHA mortar showed a decrease in setting time, while the reverse was the case for RHA-CCW mortar. In conclusion, provided adequate curing is maintained, the used of RHA-CCW gives a better performance in concrete than RHA. However, they both perform better in concrete than the plain, and can be used as additives in concrete production.

Abstract: The objective of this study was to investigate the effect of heat treatment on setting reaction and mechanical properties of tetracalcium phosphate (TTCP) and dicalcium phosphase (DCP)-based calcium phosphate cements. CPC pastes were prepared at room temperature and heated at different temperatures (from 37 to 60°C) for 10 min. Then, the preheated CPC pastes were rapidly cooled down to room temperature before further heated at 37°C until they set. Three different CPC formulations prepared from different particle sizes of TTCPs were used for the investigation. From the study, it was found that preheating could accelerate setting reaction for all CPCs according to increasing speed of hydroxyapatite (HA) conversion. The higher the preheating temperature, the faster the cements could set. However, at preheating temperature higher than 60°C longer cement setting times were observed. It may be that at high temperature some liquid content in the CPC paste evaporated, resulting in slow setting reaction rate. Compressive strengths of the cements after immersion in simulated body fluid (SBF) for 7 days increased as a result of an increase of HA conversion.

Abstract: The carbonate apatite (CO₃Ap) cement as an endodontic sealer play an essential role for endodontics treatment due to its potential to obturate root canal system as one of the most important part in endodontic treatment. Moreover, the CO₃Ap has probability of similarities with composition of root dentin. Recently, the setting time of commercial endodontic sealer has 4 hours to 1 day. Therefore, the aim of this present study is to evaluate setting time and to determine the functional group of the new material composition for endodontic sealer. CO₃Ap cement sealer was prepared by mixing dicalcium phosphate anhydrous (DCPA), vaterite and calcium hydroxide [Ca (OH)₂] with 0.2 mol/L Na₂HPO₄ containing 1% sodium carboxymethylcellulose (NaCMC) and 32 μg thymoquinone, with liquid to powder ratio of 0.6. The setting time was evaluated by Vicat needle method as describe on modification ISO 1566 for zinc phosphate cement. Five compositions of powder ratio were prepared in this study. The set CO₃Ap cement sample was evaluated by Fourier Transform Infrared Spectroscopy (FTIR) to define the functional group of the sample. Setting time evaluation indicated that the average setting time of CO₃Ap cement was 21 minutes of five compositions. The FTIR analyses revealed that the CO₃^2- groups were detected, so the results could determine as B-type CO₃Ap.The CO₃Ap cement was considered fast setting as an endodontic sealer compared to sealers made from other base and proven to have similarities with the components of root dentin.

Abstract: To reach the goal that 3D printing equipment requires and cost saving, this study used the ordinary Portland cement, mineral powder, accelerating agent and the other compound admixtures to prepare the cement-based concrete materials. The mix design, the kind and amount of accelerating agent and the dosage of compound adjusting retarders were studied to research the workability, viscosity and plasticity of the cement-based concrete materials. Facts proved that its performance are all good. And the setting time of that is adjustable of gradient form, which the range of the initial is 10-40mins and the final is 15-80mins. And the material is used to print a few simple fancy goods, which looks good, for flowerpot with roundness and square, penta-five pentagon and so on. It reflects that the speed is so far and controlled, the appearance looks knitted and layered.

Abstract: Fly ash based geopolymer normally gets the optimum strength by heat curing. This is considered as a hindrance to in-situ applications. Therefore, development of fly ash based geopolymer that suitable for ambient curing will widen the application to the concrete structure. This paper reports the results of an experimental study on setting time and development of compressive strength of class C fly ash based geopolymer paste produced in ambient curing condition. The main synthesis parameters such as water to the geopolymer solid ratio, alkali to cementitious ratio and molarity of NaOH were varied to understand their individual effect on setting time and the mechanical properties of the resulting geopolymer. The results suggested that generally the setting time increased with the NaOH molarity and the compressive strength of 59 MPa was obtained for geopolymer mixture cured at ambient temperature for 28 days with alkali to a cementitious ratio of 0.35 and 10 M NaOH. The results will be useful for developing the knowledge of the use of high calcium fly ash in producing geopolymer. This would be beneficial to the understanding the future applications of this material as new binding material.