Papers by Keyword: Hydration

Abstract: Micro-sized alumina powder is widely used in low cement high-alumina refractory castables. The hydration of calcium aluminate cement can be affected by adding micro-sized alumina powder. This work addresses the hydration of a commercial cement at 25°C with 50 wt% micro-sized alumina powder added. The hydration heat was measured by isothermal micro-calorimetry. The phase composition and microstructure of the hydration products at the designated times were studied by XRD and SEM, respectively. The results showed that micro-sized alumina powder accelerated the dissolution of CAC. The induction period of the cement hydration reduced from 13h to 4.5h, and the hydration heat within 50hs was increased from 469J/g to 587J/g with the addition of micro-sized alumina powder. The morphology of the hydrates was flocculent amorphous at the beginning, and then transformed to short rods or cubic shape with micro-sized alumina powder added.

Abstract: During research were developed ideas about the formation of C₆A₄MS phase in the aluminate clinker. The influence of the mineral and chemical composition of the raw mixture on the formation of C₆A₄MS was studied. Schemes of phase transformations providing synthesis of C₆A₄MS are proposed in this paper. Within research also have been studied the processes of hydration and hardening of aluminate phases. It was found that C₆A₄MS exhibits high hydraulic activity. Preference is given for the content of C₆A₄MS in aluminate clinkers obtained using technogenic materials.

Abstract: This research was studied the effect of 15 nm SiO₂ on the hydration behavior, hydration process and microstructure of spinel-containing high alumina cement (HAC), which is from high titanium blast furnace slag via smelting reduction method of Ti-Si-Fe making process. The results showed that with the increase of nano-SiO₂, the heat released rate of hydration and the maximum peak were decreased and advanced. Accumulation of hydration heat to release was considerably improved before 16h. Nano-SiO₂ can promote the formation of hydration products or promote the hexagonal phases CaAl₂O₄·10H₂O and Ca₂Al₂O₅·8H₂O change into cubic phase Ca₃Al₂O₆·6H₂O, which has the pozzolanic and filler effects, which The pore size distribution of the hydration products was enhanced by nano-SiO₂. At the same time, the flexural and compressive strength was increased gradually.

Abstract: This study developed lightweight concretes by using three different natural fibers from agricultural industries in Thailand which were corn husk fiber, bagasse fiber and coconut husk fiber. Low cost lightweight concretes in this study were fabricated using Ordinary Portland Cement type-1, coal fly ash, un-treated natural fibers and NaOH-treated natural fibers. The specimens were tested for bulk density, compressive strength, microstructure and deterioration. The result showed that the strongest concrete composite was obtained using 30 vol% fine coconut husk fiber in the concrete composition. The treated fibers showed an improvement in surface adhesion between cement matrix and fibers which resulted in higher compressive strength value.

Abstract: Calcium hydroxide (CH) is a by-product from hydration reaction of cement along with calcium silicate hydrate (C-S-H) gel. It helps to protect the steel reinforcements in concrete structures from corrosion process due to carbonation. The presence of calcium hydroxide provides a basic environment (pH˃10) that induces the formation of passive oxide film and keeps steel structures from corrosion. The detection and quantification of calcium hydroxide in concrete structures are important to understand the nature and state of the steel structures in concretes. In this research work, the variation of calcium hydroxide to calcium silicate ratios in cement were measured by using near-infrared spectroscopy (NIR). The first overtone of the OH groups in calcium hydroxide absorbs at 7082 cm^-1 and this absorption peak can be used as a quantitative measure of calcium hydroxide in samples. Correlation plot between second derivative absorbance intensity at 7082 cm^-1 with different mixtures of calcium hydroxide in calcium silicate base. The amount of calcium hydroxide in calcium silicate base was established. This calibration plot was used as basis for determining calcium hydroxide content in unknown concrete samples. Concrete samples for the quantitative determination of calcium hydroxide were prepared from standard cement samples and cement samples with or without pozzolan along with various water to cement ratios. The results show that all samples analyzed in this work contain calcium hydroxide in varying amounts. This variation reflects the composition of the cement and concrete samples.

Abstract: Due to the concern with the environmental impacts caused by the gases emitted by the cement industry and by the inadequate disposal of wastes generated in the sugar-alcohol industry, such as sugarcane bagasse ash (SCBA), a search for the development of new technologies, which are less aggressive to the environment and that propose feasible alternatives, began in order to reuse these wastes properly. Among these alternatives is the reuse of SCBA as partial replacement to cement or as addition to cementitious matrices. In this way, the present research has the objective of analyzing the influence of SCBA obtained by the calcination of sugarcane bagasse (SCB), at 600°C, in the process of Portland cement hydration. Initially, the SCBA was characterized physically, chemically and mineralogically, and then cement pastes with 20% and 35% substitution contents were elaborated, besides the reference paste, which were analyzed through X-ray diffraction (XRD) and thermogravimetric (TG) techniques. The results obtained show that there is a consumption of portlandite as a consequence of the use of SCBA, evidencing the pozolanicity of these ashes. In the pastes with 35% substitution content, there was an intense consumption of the portlandite, indicating, in this proportion, the pozzolanic reaction was more intense.

Abstract: Cement is a complex mixture of inorganic compounds which mainly composed of calcium silicates and calcium aluminates. Cement is mixed with water to form concrete. During the mixing calcium silicate hydrate (CSH) and calcium hydroxide are formed. The ratio of water/cement (w/c ratio) is important to obtain a mixture that gives optimum strength to the concrete. In this work, three different cement samples were mixed with water in four different ratios, including 0.35, 0.40, 0.45 and 0.55, respectively. The hydration process of cement was investigated by using near infrared (NIR) spectroscopy over a period of 28 days. The combination frequency of OH stretching and bending of water molecules gives rise to an absorption around 5200 cm^-1. This peak contains contributions of overtones from several types of water molecules in the cement. Fourth derivatives spectra of all cement samples showed three peaks in the combination band region of 5300-5100 cm^-1. These peaks indicated the presence of three distinct types of water molecules in the system. First, the characteristic peak at 5260-5240 cm^-1 represented the hydrogen bond between water molecules and silinol group of calcium silicates. This peak indicated the formation of CSH from hydration of cement. Furthermore, this peak experienced a slight red shift after a period of seven days indicating stronger hydrogen bonding of water molecules with silinol groups. The peak at 5130 cm^-1 corresponded to hydrogen bonding between water molecules and the peak at 5165 cm^-1 corresponded to hydrogen bonding between free water and bound water. The suitable w/c ratio for cement-1 is at 0.35-0.45, cement-2, and cement-3 are 0.45. In addition, real concrete sample showed two characteristic peaks at 5250 cm^-1 and 5165 cm^-1, demonstrating the presence of CSH and free water within concrete, respectively. Near infrared spectroscopy in combination with fourth derivative technique can be used to investigate the hydration chemistry of cement and concrete.

Abstract: Polymer electrolyte membranes (PEM) have a potential to become power sources in automotive industry and other household applications. PEM such as sulfonated polyetheretherketone (SPEEK) have acceptable operating temperature range but proton conductivity is dependent on amount of sulfonic groups attached to the polymer backbone (degree of sulfonation). At the same time, the sulfonic groups cause sorption of water from surrounding vapour or liquid. This factor may lead to mechanical failure if membrane absorbs too much water. Modification of PEM by adding ionic liquids (IL) may provide good proton conductivity but presence of water could also be critical factor of membrane stability as in high humidity conditions IL are washed out of membrane and replaced by water molecules. PEM with IL inclusions could be potentially used at temperatures close to water boiling point and higher as IL used in this research are thermally stable in temperatures up to 200°C.

Abstract: Dolomitic Roman cement was a widely used binder for construction purposes during the late 19^th/ early 20^th century in territory of Latvia. Because of its hydraulic properties and fast setting it was especially favorable for the usage for the cast elements of Art Nouveau style facades. The production of the material was discontinued in the middle of the 20^th century. Nevertheless, there is a need of compatible material for restoration purposes that is not currently commercially available. A compatible binder has been synthesized from mixture of dolomite flour and clay. The research gives an insight of the ongoing chemical processes during the hydration of the cement minerals in the binder. The influence of clay content in compositions and of firing temperature on the physico-chemical properties and mineralogical composition of obtained material is estimated.

Abstract: Concrete is still the most commonly used building material. The main component of concrete is Portland cement. Due to increasing use of secondary products containing zinc, the amount of zinc in the clinker or in the secondary raw materials is increasing in recent years. Portland clinker can gain zinc from solid waste or tires which are widely used as a fuel for a burning in rotary kiln. In the case of secondary raw materials, zinc may be present in the primary material, where the manufacturing process leads to its removal and concentrating to "waste" which is used in the cement industry. The biggest problem with cement doped with zinc is the retardation of hydration and decreasing of mechanical properties. The main aim of this work is describing and evaluation of zinc effect on the course of Portland cement hydration.