Papers by Keyword: Superplasticizer

Abstract: The self-consolidating concrete (SCC) become the material of choice by concrete industry due to its superior properties. However, these properties need to be verified under hot weather conditions. The paper investigates the behavior of SCC under hot weather. Six SCC mixtures were prepared under high temperatures. The SCC mixtures incorporated polycarboxylate admixture at different dosages and prolonged mixed for up to 2 hours at 30 °C and 40 °C. The cement paste was replaced with 20% of fly ash (FA). The fresh properties were investigated using slump flow, T₅₀, and VSI tests. The compressive strength was measured at 3, 7, and 28 days. The durability of SCC mixtures was evaluated by conducting rapid chloride penetration and water absorption tests.

Abstract: Self-levelling and self-consolidating concrete mixtures formed with the use of superplasticizers are worthwhile for the manufacture of reinforced concrete structures. It is important to evenly distribute not only the mixing water in the system, but also the dissociated plasticizer ions for cement dispersed compositions with plasticizing additives. It is established that the optimal sequence of loading and mixing of the components of a cement composition is not only a promising direction for intensifying the manufacture of concrete building structures, but also a tool for improving the mechanical properties of cement brick and concrete made on its basis, as well as for increasing its durability and reliability. When superplasticizers are introduced into the pre-ground cement paste, the rheological properties of the compositions are improved, as well as the structure of the hardened composites. The given article is devoted to the study of the effect of the procedural factor and the duration of mixing of highly concentrated cement compositions with the addition of a superplasticizer based on naphthalene sulfonic acid (SP C-3) on the phase composition of hardened composites during various periods of hydration. Experimental results were obtained using the X-ray phase analysis method. Tested are 15 series of samples of cement stone with W/C ratio range between 0,18 and 0,27 and SP C-3 between 0 and 1.0 % by cement weight. Comparing the phase composition of cement stone after 28 days of hardening with that of 4,5 years, it was found that at first the C₃SH₂ phase, particularly enriched with calcium oxide, is formed, which decays over time and disappears in the 4,5-year hardening amples.

Abstract: This research is concerned with a new type of ferrocement characterized by its lower density and enhanced thermal insulation. Lightweight ferrocement plates have many advantages, low weight, low cost, thermal insulation, environmental conservation. This work contain two group experimental : first different of layer ferrocement, second different of ratio aggregate to cement. The experiments were made to determined the optimum proportion of cement and lightweight aggregate (recycle thermestone ). A low W/C ratio of 0.4 was used with super plasticizer conforming to ASTM 494 Type G. The compressive strength of the mortar mixes is 20-25 MPa. The work also involved the determination of thermal properties .Thermal conductivity value of this ferrocement plate is between (0.6-0.45)W/m.K.

Abstract: Conditional quantitative criteria characterizing the shrinkage crack resistance of various concretes and a model describing the change in the proposed criteria depending on the magnitude of shrinkage deformation, creep coefficient, tensile strength kinetics and shrinkage strain kinetics for ordinary concrete and self-compacting concrete are proposed. The proposed criteria for the class C40/50 concrete have been calculated and it was shown that self-compacting concrete can potentially have higher crack resistance during shrinkage. To ensure high cracking resistance during shrinkage when choosing superplasticizers and mineral additives, attention should be paid to their effect on shrinkage, creep and E-modulus of the cement stone. It should exclude additives that increase the shrinkage and E-modulus and reduce creep of cement stone.

Abstract: Armenia is known for its large reserves of various volcanogenic tuff, pumice and slag natural porous active rocks, which due to their favorable technical properties are also interesting from the point of view of using as aggregates for foam concretes. In this research first of all the types of volcanic pumice rocks having the greatest activity and porosity are considered. At the same time, a relatively dense and chemically active lithoidal variety of pumice was used as a fine, and a highly porous Ani type pumice as a coarse aggregate. The use of coarse aggregates is unacceptable in foam concretes, but in this case, taking into account that the Ani type pumice has an average density of 350-500 kg/m², which is equivalent with foam concrete, it was decided to test as a coarse aggregate in the form of grains up to 20 mm in size. With proper dose selection, along with a positive reinforcement effect and reduction of shrinkable deformations, it will simultaneously reduce the cost of concrete by reducing the consumption of the most valuable cement component. Experience has shown that existing methods for foam concrete mixture production are not acceptable for such concretes, therefore, in order to prevent high quantity of water absorption and weighting of highly porous coarse aggregates, resulting in foam suppression and other negative consequences, there was a need to develop foam concrete mixture technology, which is presented in this research.

Abstract: Many Russian and foreign scientists have been studying the processes of hydration of cement binders, but the processes of binders hydration with the use of mineral and organic additives have not been studied enough. The question of the superplasticizers influence on binder compositions consisting of cement and various mineral fillers requires a deep and detailed study in each case. In this regard, the aim of this work is to study the processes of portland cement hydration, modified by organomineral additive. Research was carried out on the study of changes occurring during the structure formation of modified binders by infrared spectroscopy (IR).

Abstract: The development of modern construction technologies requires the development of efficient building materials with a unique property set and the improvement of existing ones. Fiber-reinforced concrete is one of the types of effective composites that meets the specified requirements, ensuring the structures operation reliability. The difficulty of achieving its maximum physical and mechanical characteristics is due to the complexity of the fiber equal distribution in the concrete matrix. Studies aimed at the optimization of the formulation and technological manufacture parameters of fiber-reinforced fine concrete, have revealed that from the perspective of obtaining products with optimal physical and mechanical characteristics, it is most feasible to introduce the agglutinant sand (cement + sand) of pre-prepared suspension from fibers, water of mixing and naphthalene formaldehyde plasticizer. Optimal dosages of input products were also revealed (basalt fiber, cement, plasticizer), which made it possible to create mixes of fine concrete and products based on it with class B25-B60 for compressive strength and Btb2,8-Btb6,0 for bending, frost resistance not less than F300.

Abstract: Usage of mineral and chemical admixtures in concrete or mortar is a usual solution to reach full compaction mainly where reinforcement blockage and the shortage of skilled labors happen. Super Plasticizers have become essential ingredients of any designed concrete mix today. Property of fresh and hardened concrete is strongly influenced by the interaction of mineral and chemical admixtures. This paper has been made to evaluate effect of heat stimulation of with two types of Polycarboxylic acid-based ether superplasticizer, pre-cast (SP2) type and ready-mix (SP1) type superplasticizer (SP) with normal Portland cement (OPC), high early strength cement (HESPC) and partially replacement of blast furnace slag (BFS) with cement 0%, 30%, 45%, and 60%. Investigated the fresh and hardened property of mortar. The superplasticizer (SP) was heated in a thermostatic chamber 70°C for 24 hours, the result shows that the heat stimulation of SP increased the fluidity, air content and flow loss, and decrease the density and compressive strength of mortar. Consequently, unitized the flow for heated and non-heated SP, and evaluate them. The air-content, density, and compressive strength were same. Besides, the flow loss was affected by many factors type of cement type of SP and heat stimulation technique of SP amount of BFS. By heat stimulation technique and increasing the amount of BFS caused to decrease the flow loss. The SP1 improve the fluidity and flow loss of mortar than SP2 in all conditions. Heat stimulation technique of SP with HESPC cement doesn’t change the fresh property of mortar. The compressive strength of HESPC was increased than OPC cement. Furthermore, by increasing the amount of BFS increased the fluidity and decreased the compressive strength and effect of heating on fluidity. The water-cement ratio was 30% and sand cement ratio was 2:1. Blast furnace slag (BFS) cause to improve the fluidity of mortar. However, by increasing the amount of BFS the compressive strength and effect of heat stimulation and flow loss was decreased.

Abstract: A complex organomineral additive based on local raw materials (diatomite), superplasticizer and accelerator for sodium sulfate hardening has been developed. The possibility of using activated diatomite in the composition of concrete instead of microsilica with activation of the sodium sulfate hardening process is shown. The results of the effect of additives on the composition of the hydrated phases of cement systems, the processes of structure formation and hardening of cement materials, the effect of a complex additive on the strength of concrete are given. The achievement of high strength parameters of concretes, including those with a lower cement consumption, is ensured by introducing into the concrete mix fine-dispersed mineral components that promote the creation of a rheologically active matrix and increase the effectiveness of super-and hyperplasticizers.

Abstract: The applicability of a proposed model similar to a well-known Hirsch's model for predicting the E-modulus of concrete and the creep coefficient of concrete depending on the composition of the concrete, the properties of the components of concrete mix and the possible effect of the superplasticizer on the deformation properties of cement stone both under short-term and long-term loading is proved. Value ​​of the E-modulus of self-compacting concrete can be reduced to 20% with respect to the ordinary concrete of equal compressive strength, which is confirmed by the model calculation data and some experimental data. For concretes with mineral additives, the influence of mineral additives on the E-modulus was not established. Both an increase and decrease in the E-modulus is possible. The effect depends on the type of additive. The creep coefficient of self-compacting concrete, obtained by calculation according to the model, due to the increased content of cement stone and the possible influence of superplasticizer on the creep of cement stone, can be from 1.3 to 1.8 of the coefficient of creep of ordinary concrete. This result agrees well with some experimental data. The creep coefficient of concrete with mineral additives (silica fume, white ash and metakaolin), obtained by calculation according to the model, can be from 0.5 to 0.6 of the coefficient of creep of ordinary concrete. This result agrees well with some experimental data.