Types Of Chemical Admixtures Research Articles

Use of nanocrystal seeding chemical admixture in improving Portland cement strength development: application for precast concrete industry

This paper summarises an investigation into the potential advantages to the precast concrete industry of using a new ‘seeding’ type of chemical admixture in Portland cement (PC) based concrete mixes. Results indicated that the addition of 2–4% nanocrystal seeding chemical (NCS) admixture by weight of PC can provide a doubling of early strength, particularly at 6 and 12 h. This strength gain could lead to the turnover of moulds in precast concrete plants being completed twice in 24 h, thus increasing production capacity. Isothermal conduction calorimetry, X-ray diffraction and thermogravimetric analysis techniques were used to investigate the reasons for the improvement in compressive strength development. Results indicated that the increase in early compressive strength is due to an acceleration of early hydration of PC in presence of the NCS. Indeed, after 6 h, the degree of hydration was more than 50% greater when NCS was used. This paper also highlights the possibility of the NCS chemical admixture being used in conjunction with supplementary cementitious materials (SCMs) in PC blended concrete mixes. 2% NCS was added to a blend containing 70% PC and 30% ground granulated blast furnace slag (GGBS). Results indicated that early strength values were greater compared to the blend without NCS and comparable to the 100% PC mix.

Effect of chemical admixtures on loaded reinforced concrete columns in fire

This investigation reports on a comparative study of the residual capacity at elevated temperature of loaded reinforced concrete column specimens containing different types of chemical admixtures and coarse aggregate. Three types of aggregate were employed named gravel, dolomite and basalt as well as three types of admixtures named superplasticizer, setting retarder and setting accelerator. 12 concrete mixes were prepared. Each mix contained two column specimens. One of them was tested at ambient temperature to determine its load capacity and the second was loaded with working load and exposed to 650°C for 30 minutes. During heating, the temperature at different locations on the mid height section of the specimen were recorded every 5 minutes. The results showed better performance of basalt and dolomite concretes without admixtures, after firing. Adversely, when admixtures are included, gravel concrete performs better than basalt and dolomite concretes, after firing.

Effect of content and particle size distribution of coarse aggregate on the compressive strength of concrete

Coarse aggregate fraction is known to strongly influence both fresh and hardened concrete’s properties. Consequently, selection of both content and particle size distribution (PSD) for concrete mixture is an important issue regarding the predicted performance of concrete. In the present study, and based on previous results obtained, four granular fractions were combined in different proportions in order to investigate the effect of the PSD of aggregate on the properties of concrete. Two types of chemical admixtures, water reducer agent (WRA) and superplasticizer (HRWRA) were used to decrease the water-cement ratio (w/c) which ranges from 0.58 to 0.40. Compressive strength function the PSD of coarse aggregate was determined at 7, 14 and 28 days. Results have revealed that the mixtures without chemical admixture made with a ternary combination of granular fraction and having a maximum size of 25 mm, that assures a continuous granular size distribution, have shown the highest compressive strength. However, decreasing the w/c by the inclusion of WRA or HRWRA requires a decrease of the maximum size of coarse aggregate and some adjustment in the granular size distribution system. The binary granular system has led to the highest compressive strength when dealing with low w/c.

Utilization of Chemical Admixtures for Concrete Production

Nowadays especially, in ready-mixed concrete plants utilization of chemical admixtures is very common. Chemical admixtures improve the properties of concrete. If they used unconsciously results should be detrimental. A public survey has performed in Eskisehir to determine the types of chemical admixtures, which are used in concrete companies, the consciousness of using chemical admixtures, their experiences and suggestions for chemical admixtures. It can be seen from public survey results plasticizer are common for concrete production than other admixtures. Before utilization of chemical admixtures concrete producers perform pre-experimental studies. According to these studies the admixture content is determined for production. It can be seen from results, all ready-mix concrete producers uses chemical admixtures in concrete production.

Mechanical Properties of High-Strength Concrete Incorporating Carrier Fluidifying Agent

Carrier fluidifying agent (CFA) is a type of chemical admixture that is able to retain the workability of high-strength concrete. It has been found that, apart from being able to retain the workability of high-strength concrete for up to 2 hours, CFA marginally improved the mechanical properties of high-strength concrete. In this study, the mechanical properties of high-strength concrete with and without CFA are investigated and compared in terms of mechanical strengths, such as compressive, splitting tensile, flexural, shear property, and bond-to-reinforcement, as well as deformation characteristics, such as static modulus of elasticity, Poisson's ratio, and creep of concrete.

Chemical Admixtures for Concrete

Following the substantial increase in the use of chemical admixtures in concrete, the book provides information on materials of this type. Details are given of the specification, use and design of concrete mixtures with information on the types, mode of action, effect and application of the major types of chemical admixtures in the following sections: water-reducing agents; air-entraining agents; concrete waterproofers; accelerators; application of admixtures; and, analysis of hardened concrete for admixture type and quantity. (TRRL)