Effects Of Various Admixtures Research Articles

Influence of various admixtures on energy absorption characteristics of foam concrete measured using one dimensional strain analysis test

Foam concrete (FC) (a light weight cellular concrete) has recently clutched the interest of military engineering due to its special attributes such as cushioning behavior and energy absorption. However, only a very few investigations on the mechanical performance of FC and its energy absorption characteristics are reported in the literature. This study examines the effects of the addition of polypropylene fibres, fly ash (as filler replacement), and silica fume (as binder replacement) on fresh state features (stability and consistency), mechanical properties, and energy absorption characteristics. The individual and combination effects of various admixtures are studied experimentally. Hingot surfactant was used to produce FC mixes of target density 1000 kg/m3 with water to solid ratio of 0.3. Comparative analysis of various mixes showed that the fiber-reinforced fly ash mix showed the highest mechanical strength due to the bonding of fibres with the matrix, thus demonstrating synergistic behavior. Further, one-dimensional compression strain testing methodology was employed to study the energy absorption characteristics of FC. Experimental outcomes showed that the energy absorption values depend on two important components which are resistance against plastic yield, referred to as ductility, and resistance against damage referred to as the strength of the material. The incorporation of fibres enhanced the ductility of the specimen by acting as a toughening agent, whereas fly ash substitution contributed to enhancement of strength of the specimen due to pozzolanic and filler effects. Hence the combination mix with FA and PP (CMFP) showed significant improvement of 34.6% in energy absorption when compared to control mix.

Pregled čimbenika koji utječu na svojstva poroznog betona

Pervious concrete is an environment friendly solution for eliminating imperviousness-related drawbacks of conventional concrete. Pervious concrete mixes are predominantly composed of cement, coarse aggregate, and water. The partial or complete elimination of fine aggregate results in porous structure, which influences performance of pervious concrete. This article is aimed at reviewing major factors involved in the design of pervious concrete mixes, namely the compaction, aggregate to cementitious material ratio (ACR), sand fraction, water to cementitious material ratio (w/cm), size of coarse aggregate, and void ratio or porosity. The effects of various admixtures, replacement materials, and fibres, are also discussed. The results indicate that pervious concrete acts as an effective medium in promoting the sustainability of urban environments due to its multi-aspectual benefits.

A Review on Study on Effect of Various Admixtures on Geotechnical Properties of Expansive Soils

Objectives: Waste materials can be used as geotechnical admixtures to improve geotechnical properties of black cotton soils as well as curb environmental degradation. Methods: The aim of this paper is to provide a clear understanding of the effect of geotechnical admixtures on the properties of expansive soils through selective reference to some of the literature. Experimental observations such as maximum dry density, optimum moisture content, California bearing ratio and unconfined compressive strength are reviewed. A comparative study is based on the proposed optimum combinations of admixtures and the geotechnical properties of expansive soil. Findings: Addition of geotechnical admixtures alters the physical and compaction characteristics of cohesive soils. Through thorough comparative studies of the existing researches it can be inferred that the combinations of admixtures and expansive soil improve the CBR value, UCS and decrease swelling index of soft soils to an acceptable range and aid in achieving economic design of pavement. Applications: • Stabilization of black cotton soil. • Optimum use of admixtures to enhance the geotechnical properties of black cotton soil. • Construction of pavements over black cotton soil. • Slope stability of embankment construction over black cotton soil.

Effect of various admixtures on the properties of Mn-substituted cordierite

The effect of various admixtures (graphite, sawdust, mullite–silica fiber, vermiculite, boric acid, different size fractions of cordierite, corundum microspheres) in the cordierite stock (mixture of talc, clay, manganese oxide, and aluminum hydroxide) on the formation of Mn-substituted cordierite has been investigated. The admixtures exert an effect on the degree of cordierite formation, on the impurity phase content of the product (including its Mn2O3 content), on the surface concentration of manganese cations, on their oxidation state, on the texture of the catalysts, and on their ammonia oxidation activity. The highest NOx yield is observed with the catalysts containing a coarse fraction of cordierite and corundum microspheres, which are characterized by a high surface concentration of oxidized manganese cations and have large transport pores.

RILEM draft recommendation: TC-242-MDC multi-decade creep and shrinkage of concrete: material model and structural analysis*

In response to the continuously advancing concrete technology, a new prediction model for creep and shrinkage is presented. This model, named B4, builds on the theoretically justified model B3, which is a RILEM recommendation from 1996. Improvements to the model allow for enhanced multi-decade prediction, distinguish between the drying and autogenous shrinkage, and introduce new equations and parameters to capture the effects of various admixtures and aggregate types. The development and justification of the model is described in three companion articles which follow.

Effects of admixtures on the rheological properties of high-performance wet-mix shotcrete mixtures

This study investigates the effects of various admixtures on the rheological properties of high-performance wet-mix shotcrete (HPWMS) in an attempt to resolve practical issues faced in conventional wet-mix shotcrete processing. The admixtures used in this study were silica fume, air-entraining agent (AEA), superplasticizer, synthetic fiber, powdered polymer, and a viscosity agent. Representative rheological properties such as yield stress and plastic viscosity were measured using an IBB rheometer to evaluate the pumpability and shootability of HPWMS with varying admixture types and contents. The results demonstrated that the use of AEA tended to reduce both flow resistance and torque viscosity of HPWMS almost proportionally. A superplasticizer had a relatively greater impact on the flow resistance rather than torque viscosity. Also, it was observed that silica fume led to a remarkable increase in flow resistance while it slightly reduced torque viscosity. This behavior trend indicates that silica fume is quite effective in enhancing the rheological properties of HPWMS, particularly in terms of shootability and pumpability.

Effects of various admixtures and shear keys in wood–concrete composite beams

Wood–concrete composite beams are a layered system, which essentially utilize a concrete layer in compression and a wood layer in tension. This layered system offers a way to construct or rehabilitate wood floors in historic timber structures while increasing the floors’ stiffness and load carrying capacity. This research paper investigates past problems with poor consolidation of the concrete, transverse shrinkage cracks in the concrete, swelling of the wood, moisture loss from the concrete, and the resulting reduced composite efficiency. The research presented herein describes how these problems can be mitigated and thereby increase the composite efficiency of the wood–concrete composite system. By painting the specimens with a water proofing paint, the swelling of the wood can be reduced, which helps to maintain a tight interface between the wood and concrete. To improve consolidation, a self-leveling concrete was designed with a 28-day compressive strength of 34.5 MPa and a slump of 279.4 mm. Nylon fibers and Type I steel fibers were used as admixtures to the fresh concrete to determine their effect on the composite efficiency and the reduction of shrinkage cracks. Twelve full size specimens were constructed and tested to failure. It was found that the most common mode of failure was combined bending and tension at mid span in the wood. An average composite efficiency of 83.4% was reached in the full size test specimens when placed in four point bending.

Assessing the Efficiency of Chemical and Mineral Admixtures in Early Cement Hydration

A procedure is proposed for evaluating the efficiency of chemical and mineral admixtures in early cement hydration with the use of calorimetric data and with allowance made for the selective effect of admixtures on the hardening process. The concepts of admixture efficiency and admixture–cement compatibility are formulated and are shown to be of practical importance. The proposed approach is substantiated using thermokinetic results on the effects of various admixtures on the hydration of different cements, and the underlying mechanisms are discussed.

A thermal study of polymineral clays of the Gzhel' deposit

A thermal analysis of clays of the Gzhel' deposit is performed and their mineral composition is established. The effect of various admixtures and minerals and the dispersity on the behavior of the clays during heating is described.

Effect of various admixtures on the particle size distribution of cement determined with the aid of laser particle analyser

The paper presents an attempt on the determination of dispersability of cement particles in the presence of various admixtures (Superplasticizers, accelerator, retardars etc.) using a commercially available laser particle size analyser. The change in particle size during hydration after various intervals of time has been determined in this study. This also brings out a quick efficacy evaluation method for various admixtures by observing the reduction in particle size as compared to the size of unhydrated cement particles originally taken for experiment. This paper describes the results of a number of particle size distribution studies made with seven admixtures alongwith one without admixture for particle sizes distribution and surface areas using a commercially available Indian OPC grade 43 produced by M/S Dalmia Cements.

A comparison between semi-isothermal and semi-adiabatic calorimetry of retarded cement mixes

Synopsis A comparative study has been made of the effect of three retarding admixtures, representing the main commercially available materials, on the rate of heat evolution from hydrating cement. Two methods of calorimetry have been used, semi-isothermal and semi-adiabatic, to enable a preliminary assessment to be made of any major differences between the methods. Because of experimental differences, the results from the two test methods are not directly comparable, but significant differences are seen between the two sets of data. This emphasizes the need to take into account the effect of temperature rise during cement hydration and the differing effects of various admixtures.

Estimation of Ca(OH)2 and Mg(OH)2 — Implications in Cement Chemistry

AbstractPortland cement, hydrated Portland cement, magnesium oxychloride, magnesium oxysulphate and plasters are inorganic cementitious systems in which different amounts of MgO, CaO, Ca(OH)2 and Mg(OH)2 are present. Identifying and estimating the Ca‐ and Mg‐oxides and hydroxides by DTA provides information that can, in turn, be used for studying the mechanism of hydration of CaO, reactivity of calcium silicates, the relevance of the autoclave test for determining the unsoundness of cements, interactions occurring in polymer‐impregnated cement, the effect of various admixtures on the hydration kinetics of cement and cement compounds, the contribution of Ca(OH)2 to the physico‐mechanical properties of cement, the composition of the hydrated silicates, mechanism of hydration, chemical activity of blended cements, strength development in magnesium‐oxychloride and magnesium‐oxysulphate cements and causes of failure of gypsum plasters.

Influence of Water-Reducing Admixtures on Properties of Cement Paste—A Miniature Slump Test

Abstract A miniature slump test has been developed for the evaluation of the influence of water-reducing admixtures on the workability of neat portland cement pastes. Resulting paste pat areas rather than heights are measured, and the results are expressed as the percentage of water reduction. Relative effects of various admixtures on a portland cement are illustrated, and influences of specific admixtures on different cements are also shown. Effects of different superwater-reducing admixtures and combinations of ordinary and superwater-reducing admixtures are compared. The mini-slump method has also been used for the evaluation of the loss of workability (slump loss) with time for various admixtures and admixture combinations. The simplicity of the method facilitates accurate and effective evaluation of water-reducing admixtures.