Effect Of Chemical Admixtures Research Articles

Light Weight Geopolymer Paste Made with Sidoarjo Mud (Lusi)

This paper presents the efforts of how to use the solid form of Sidoarjo mud as a base material of lightweight-geopolymer paste. The mud, which is called Lusi was mixed with a class F fly ash. Some experimental results have shown that mixing mud with fly ash and alkali was potential to become a binder in concrete, instead of Portland cement. Alkaline solutions used in the mixture were NaOH of 12 M and 14 M and Na2SiO3combined in the ratio of 1:2.5 by weight. Aluminum powder was applied as a foaming agent. It showed that the strength of paste made with mixing Sidoarjo mud and fly ash was influenced by mud content. The effect of chemical admixture and curing temperature was observed as well. A steam curing method at 60°C was applied to the paste for three and six hours. Test results showed that the compressive strength of the paste varied with the concentration of alkaline solution, mud content, admixture and curing temperature. The maximum strength of the lightweight paste at 21 days was 2.8 MPa with the density of 722 kg/m3.

The Effect of Chemical Admixtures on Removal of Scattered Dust

One of the important problems associated with building demolition is the dust generated during the work. The only way to reduce the demolition dust is to use a dust net during water spraying. However, it is difficult to supply the necessary amount of water to remove demolition dust, thus making it difficult to apply this method on a demolition site. This work attempted to find an alternative approach to dust removal by incorporating surfactant and high range AE water reducer in the water being sprayed. Through the experiment, it was found that the addition of surfactant did not contribute to the removal of demolition dust. However, the use of high range AE water reducer showed better performance than spraying plain water, indicating that some amount of demolition dust had been adsorbed on the high range AE water reducer.

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.

Fingerprinting of Chemical Admixtures in Fresh Portland Cement Concrete by Portable Infrared Spectrometer

The ongoing second SHRP 2 R06-B project entitled Evaluating Applications of Field Spectroscopy Devices to Fingerprint Commonly Used Construction Materials conducted at the University of Connecticut targets, among other objectives, the identification and quantification of chemical admixtures in portland cement concrete (PCC). The two specific objectives for the PCC study are (a) the applicability of portable infrared spectrometers for identification of the admixtures in fresh concrete under field conditions and (b) the feasibility of tracking interaction between hydration products during PCC setting. In the first phase of the study, four admixtures (air entrainer, retarder, accelerator, and super-plasticizer) were tested to establish their chemical signature in the infrared and ultraviolet regions of the electromagnetic spectrum. The fingerprinting of the admixtures was performed with a portable attenuated total reflection (ATR) Fourier transform infrared spectrometer. The second phase concerned evaluating freshly mixed PCC samples prepared with each admixture separately in the amount prescribed by the manufacturer. Chemical changes in the PCC samples were tracked over the 6-h period by the portable ATR spectrometer. Quantitative analysis of the ATR spectra allowed for evaluating the effect of chemical admixtures on hydration activity in PCC.

Effect of chemical admixtures on properties of high-calcium fly ash geopolymer

Owing to the high viscosity of sodium silicate solution, fly ash geopolymer has the problems of low workability and rapid setting time. Therefore, the effect of chemical admixtures on the properties of fly ash geopolymer was studied to overcome the rapid set of the geopolymer in this paper. High-calcium fly ash and alkaline solution were used as starting materials to synthesize the geopolymer. Calcium chloride, calcium sulfate, sodium sulfate, and sucrose at dosages of 1wt% and 2wt% of fly ash were selected as admixtures based on concrete knowledge to improve the properties of the geopolymer. The setting time, compressive strength, and degree of reaction were recorded, and the microstructure was examined. The results show that calcium chloride significantly shortens both the initial and final setting times of the geopolymer paste. In addition, sucrose also delays the final setting time significantly. The degrees of reaction of fly ash in the geopolymer paste with the admixtures are all higher than those of the control paste. This contributes to the obvious increases in compressive strength.

Effect of Chemical Admixtures on Silicate Structure of Hydrated Portland Cement

Effect of Chemical Admixtures on Silicate Structure of Hydrated Portland Cement

Effect of Chemical Admixtures on Rheology of Cement Paste at High Temperature

Abstract Placement of cement-based materials in hot weather conditions encounters many problems due to the rapid evaporation of mixing water and the accelerated hydration of cement. Such materials are also adversely affected at elevated temperatures by an increased water demand, shorter setting time, and more rapid slump loss. These problems can be mitigated using adequate chemical admixtures. However, technical data on such admixtures are commonly developed at normal temperatures, and there is a real need to investigate their performance at hot temperatures. In the current research, the rheological properties of portland cement pastes with a water-cement ratio (w/c) of 0.35 and 0.50 are investigated at different temperatures in the range of 20 to 45°C using an advanced shear-stress/shear-strain controlled rheometer. The influence of water-reducing and retarding admixture, polycarboxylate, naphthalene sulfonate, and melamine-based high-range water-reducing admixtures (HRWR) in addition to mid-range water-reducing admixtures (MRWR) on the rheological properties of cement paste at various temperatures was also examined. The paper aims at formulating recommendations for the effective use of chemical admixtures at high temperature, which should enhance the rheological properties of cement-based materials in hot weather conditions.

Performance of concretes produced with superplasticizer

AbstractNowadays, additive chemical substances are used in the production of high‐performance concrete composites. These additives increase the fresh workability of concrete by decreasing the water/cement (W/C) ratio. The aim of this study was to examine the effects of water‐soluble polymers on concrete performance. For this purpose concretes with and without additives were produced with W/C values of 0.52, 0.56, and 0.60. Chemical admixtures such as naphthalene formaldehyde sulfonate (N), melamine formaldehyde sulfonate (S), and a hyperplasticizers admixture (a special type of melamine sulfonated polymer) (H) were used in concrete. The amounts of these admixtures were at a ratio of 0.3, 0.5, and 1.0 wt % of the cement's weight. Experiments assessing slump, VeBe, percentage of air, and unit weight were done for comparison with the test results of the characteristics of fresh concrete with and without admixtures. The compressive strength of concretes was determined at 7, 28, and 56 days. The effects of chemical admixtures were studied by comparing the properties of fresh and hardened concrete samples with and without admixtures. When the W/C ratios were 0.56, 0.60, and H was 1 wt %, the biggest slump was obtained and found to be 22 cm. Concrete with a W/C ratio of 0.52 and H of 1% has the highest compressive strength. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3214–3219, 2007

Utilization of coal combustion byproducts in building blocks

Some mechanical and durability properties of composite material produced with by-products of Orhaneli power plant (flue gas desulfurization sludge, fly ash and bottom ash), cement and hydrated lime were investigated. To improve the mechanical properties (compressive and flexural strength) of this material, steam curing was applied and the effect of chemical admixture (high water reducing agent) was investigated. Some physical properties and water resistance of the mixtures were also determined. Furthermore, microstructure of the specimens was investigated using scanning electron microscopy. Finally, to produce construction elements, prototypes of building blocks were manufactured by using some of these mixtures. All kind of power plant wastes (flue gas desulfurization sludge, fly ash, bottom ash) can be utilized with these mixtures, which consist of 90% of coal combustion byproducts. It seems to be a promising material for composite construction elements such as building blocks.

Energy absorption of nanoporous silica particles in aqueous solutions of sodium chloride

An experimental study is carried out on the effect of chemical admixtures, particularly sodium chloride, on the energy absorption behaviour of a hydrophobic nanoporous silica. As the pressure increases, once the capillary effect is overcome, the liquid is forced into the nanopores; and when the pressure is reduced, outflow is difficult, resulting in a pronounced hysteresis. The inflow pressure and the specific absorbed energy are strongly dependent on the sodium chloride concentration, providing a promising way to adjust the system performance.

Investigation of structural properties associated with alkali–silica reaction by means of macro- and micro-structural analysis

Structural properties associated with alkali–silica reaction were systematically investigated by means of macro-structural accelerated mortar prism expansion levels testing, combined with micro-structural analysis. One part of this study is to determine the reactivity of the aggregate by means of accelerated mortar bar tests, and also to evaluate perlite aggregate constituents, especially the presence of deleterious components and find main causes of the alkali–silica reaction, which was based on the petrographic studies by optical microscope and the implication of X-ray diffraction on the aggregate. Results implied that the aggregate was highly alkali–silica reactive and the main micro-crystalline quartz-intermediate character and matrix that is mainly composed of chalcedony are potentially suitable for alkali–silica reaction. The other part is to study the long-term effect of lithium salts against alkali–silica reaction by testing accelerated mortar prism expansion levels. The macro-structural results were also consistent with the micro-structural mechanisms of alkali–silica reaction of mortar prisms containing this aggregate and the effect of chemical admixtures by means of the methods of scanning electron microscope–X-ray energy-dispersive spectroscopy and X-ray diffraction. It was indicated by these techniques that lithium salts, which were introduced into concrete containing reactive aggregate at the mixing stage, suppressed the alkali–silica reaction by producing non-expansive crystalline materials.

The effect of chemical admixtures and mineral additives on the properties of self-compacting mortars

Mortar serves as the basis for the workability properties of self-compacting concrete (SCC) and these properties could be assessed by self-compacting mortars (SCM). In fact, assessing the properties of SCM is an integral part of SCC design. The objective of this study was to evaluate the effectiveness of various mineral additives and chemical admixtures in producing SCMs. For this purpose, four mineral additives (fly ash, brick powder, limestone powder, and kaolinite), three superplasticizers (SP), and two viscosity modifying admixtures (VMA) were used. Within the scope of the experimental program, 43 mixtures of SCM were prepared keeping the amount of mixing water and total powder content (portland cement and mineral additives) constant. Workability of the fresh mortar was determined using mini V-funnel and mini slump flow tests. The setting time of the mortars, were also determined. The hardened properties that were determined included ultrasonic pulse velocity and strength determined at 28 and 56 days. It was concluded that among the mineral additives used, fly ash and limestone powder significantly increased the workability of SCMs. On the other hand, especially fly ash significantly increased the setting time of the mortars, which can, however, be eliminated through the use of ternary mixtures, such as mixing fly ash with limestone powder. The two polycarboxyl based SPs yield approximately the same workability and the melamine formaldehyde based SP was not as effective as the other two.

Effect of Chemical Admixtures on the Engineering Properties of Tropical Peat Soils

This research describes a study on the effect of chemical (cement and lime) admixtures on the index and engineering properties (compaction and unconfined strength) of tropical peat soils. The ordinary Portland cement and hydrated lime were used. The amounts cement and lime added to the peat soil sample, as a percentage of the dry soil mass was in the range of 5-15% and 5-25%, respectively. The results of the study show that the addition of the chemical admixture, cement and lime, can improve the engineering properties of tropical peat soils. The soil liquid limit is found to decrease with an increase in the cement and lime content. The soil maximum dry density is found to increase while the optimum water content is found to decrease with an increase in the cement and lime content. The unconfined compressive strength of the soil is found to increase significantly with increase in cement and lime content, especially after a long curing period. However it is also found that higher organic content of the soil negate the positive effect of the cement and lime in altering (improving) the mechanical properties of the soil. When comparing the performance of the cement and lime as a chemical admixture for the tropical peat soil, the ordinary Portland cement appears to perform better than the hydrated lime.

Effect of chemical admixtures on rheological parameters and stability of fresh lightweight aggregate concrete

This paper presents results of an experimental study on the effect of a superplasticiser and an air-entraining admixture (AEA) on the rheological behaviour of fresh lightweight aggregate concrete and the stability of the concrete under vibration. The results indicated that an increase in superplasticiser content in the concrete reduced the yield stress, but did not have a significant effect on the plastic viscosity. The increase in air content in the concrete by using AEA reduced the plastic viscosity. The yield stress, however, was reduced only when the AEA was first introduced. Further increase in the AEA content did not have a significant effect on the yield stress of the fresh concrete. When the concrete experienced vibration, the segregation resistance decreased with a decrease in both the yield stress and the plastic viscosity. However, the effect was more pronounced with the decrease in yield stress.

Effect of chemical admixtures on rheological parameters and stability of fresh lightweight aggregate concrete

This paper presents results of an experimental study on the effect of a superplasticiser and an air-entraining admixture (AEA) on the rheological behaviour of fresh lightweight aggregate concrete and the stability of the concrete under vibration. The results indicated that an increase in superplasticiser content in the concrete reduced the yield stress, but did not have a significant effect on the plastic viscosity. The increase in air content in the concrete by using AEA reduced the plastic viscosity. The yield stress, however, was reduced only when the AEA was first introduced. Further increase in the AEA content did not have a significant effect on the yield stress of the fresh concrete. When the concrete experienced vibration, the segregation resistance decreased with a decrease in both the yield stress and the plastic viscosity. However, the effect was more pronounced with the decrease in yield stress.

Effect of Chemical Admixtures on Workability and Strength Properties of Prolonged Agitated Concrete

A lignosulfonate-based water reducer, a dextrin-based water reducer, and a gluconate-based retarder were used in concretes which were mixed continuously in the drum of a truck mixer, and the slump measurements were carried out at certain time intervals. It was found that at any time, the slump loss in gluconate-based retarder and combined lignosulfonate and gluconate mixes was less than those of other mixes. The setting times of samples taken after prolonged mixing, as well as after retempering, were also compared with those of initial ones. Compressive and flexural strengths of samples taken initially and after different agitation times were determined. The strength change obtained after prolonged agitation was slight, but retempering by water to bring the workability to the initial level reduced the strengths; however, the strength loss in gluconate retarder-added mixes was smaller than those of others. The bond strength between reinforcing bar and reference mix was also compared with that of gluconate retarder mix.

Effect of chemical admixtures on the expansion of shrinkage-compensating cement containing a pre-hydrated high alumina cement — based expansive additive

The effect of chemical admixtures on ettringite formation and expansion of expansive cement containing a pre-hydrated high alumina cement — based additive (H-HAC) is discussed. Nine chemical admixtures including surfactants, accelerators, retarders and a bonding agent were investigated. Compacted samples were used to study the effect of chemical admixtures on relevant hydration reactions. Normally mixed paste samples were also used to study chemical and surface — chemical effects. The effect of admixtures on ettringite formation and reaction of gypsum at early hydration times was followed by XRD analysis of high w c wet samples containing large amounts of expansive additive. Suggestions are given for the control of ettringite formation and expansion in expansive cement — based systems.

Early Age Behavior of Portland Cement Paste

In this paper, tests for consistency, bleeding, and setting of portland cement pastes with and without addition of chemical admixtures are reported. On the basis of the results obtained from these tests and previous understanding, some innovative concepts concerning the nature and the mechanism of the behavior of portland cement paste in its early age are discussed. The area covered in this report includes consistency, fluidity, plasticizing effect of chemical admixtures, settling and bleeding, setting and false setting of cement pastes, and slump loss and retempering of concrete mixtures.

Effects of admixtures and alkali compounds on alkali aggregate reaction

Tests of mortar bar expansion are reported with bronzite andesite reactive aggregate found in Japan. The effects of chemical admixtures, sodium alkalis and of fly ash and slag on expansion are presented. Chemical admixtures appeared to reduce expansion whereas alkali compounds caused large expansion with sodium salts more aggressive than potassium salts. Fly ash and slag were found effective in controlling expansion.

The zeta-potential of cement

Zeta-potential measurements provide new informations on cement hydration, gel structure formation and the effects of chemical admixtures. The formation and significance of a zeta-potential of cement in aqueous suspension is discussed with respect to the hydration of cement and some new data on the zeta-potential of cement and fly ash under various conditions are presented.