Composition Of Concrete Mixture Research Articles

Restrained concrete shrinkage in composite trusses

An analytical approach to compute restrained shrinkage effects on composite concrete deck – steel truss members is presented and validated using strains and deflections obtained by Brattland and Kennedy, who in 1986 tested two full-scale (11.8 m × 2.35 m in plan) composite trusses and companion drying specimens for approximately 90 d. The test-to-predicted ratios for these quantities are excellent, with a mean value of 0.89 and a coefficient of variation of 0.11. It is also demonstrated that (1) single test specimens with a single drying face exhibit a large gradient of free shrinkage strain across the depth of the specimen that must be properly considered in the analysis; (2) shrinkage parameters estimated using generic rules based on the concrete mixture composition are not realistic for the particular mix used by Brattland and Kennedy; and (3) history-independent analysis methods, as described in Annex H of CSA S16-09, do not accurately predict the slab strains and truss deflections observed by Brattland and Kennedy unless the variation of the free shrinkage strain with slab depth, tensile creep, and concrete modulus of elasticity are properly accounted for.

Evaluation of Recycled Aggregate Concrete Cracking through Ring Test

Cracks can reduce the service life of a concrete structure by allowing aggressive agents to penetrate through it in easy ways. Free shrinkage evaluation alone is not enough to determine if cracking can be expected in a structure since concrete creep behaviour, stiffness and toughness also influence the potential for cracking. Consequently, it is rather interesting to perform restrained shrinkage tests, such as the ring test according to ASTM C 1581–04. The testing procedure involves concrete ring specimens restrained by an inner steel ring on which strain gauges are placed to determine the age of cracking, since abrupt changes in the steel strain occur when concrete is cracked. Both the ring test and free shrinkage test should be carried out in the same exposure conditions, 21°C and 50% relative humidity. Moreover, compressive and tensile strengths of concrete were evaluated on cubic specimens at the time of its cracking and up to 28 days of curing. By means of analytical and numerical models of the ring specimen, some useful information on the stress induced in the material and on the tensile creep behaviour of concrete can be extrapolated thus allowing to better interpret the experimental results. This experimental procedure enables to study the influence of concrete mixture composition on the potential for early-age cracking of concrete. In particular, in this work the influence on early-age cracking of recycled-concrete aggregate partially replacing virgin sand was tested.

Estimation of slump value and Bingham parameters of fresh concrete mixture composition with artificial neural network modelling

High performance is the most important expectation from concrete which is commonly used in today’s construction technology. To form a high performance concrete “HPC”, two fundamental properties are required. These properties are optimization of the materials used to form the concrete and the workability of fresh concrete during shaping. Many scientists have used rheological properties in conjunction with Bingham model to determine the workability of fresh concrete. Bingham model is represented by two parameters: yield stress and plastic viscosity. Even though, many models are developed to explain rheological properties, there is no acceptable easy to use method. In this study, artificial neural network “ANN” is used to determine the rheological properties of fresh concrete. Ferraris and de Larrard’s experimental slump, yield stress and viscosity data from different composed concretes is used in this study. Slump, yield stress and viscosity are estimated with respect to mixture design parameters. Obtained results from this study indicates that ANN is a utilizable method to determine the rheological proporties (Bingham model) of fresh concrete. Key words: Fresh concrete, Bingham flow, slump value, artificial neural network.

Effects of Cement and Water Contents on Adiabatic Temperature Rise of Concrete

Concrete mixture composition and proportions, in which cement content should play a major role, are factors on which, during curing, concrete temperature rise depends. There would not be full cement hydration if there would be relatively low water content, and cement would also be significantly affected by water content. An experimental program designed to investigate cement and water content combined effects through adiabatic temperature rise measurement of concrete mixtures with different mixture proportions is reported on by the authors. For concrete mixture adiabatic temperature rise measurement, a newly developed semi-adiabatic curing test method was employed that applied heat loss compensation. That the adiabatic temperature rise for a given paste volume would be highest at a 0.36 water-cement (w/c) ratio is revealed in the results, therefore, there is not necessarily a higher adiabatic temperature rise in higher strength concrete. As the w/c decreases, furthermore, the degree of hydration would gradually decrease. Design charts and formulas for adiabatic temperature rise, heat generation, and degree of hydration prediction have been developed based on these results for concrete mixtures with a 0.28 to 0.48 w/c range.

Relationship Between Indentation Hardness and Water to Cement Ratio of Hardened Mortar and Concrete

Abstract Accurately estimating the water-to-cementitious materials ratio (w/cm) of hardened concrete is one of the most difficult tasks frequently requested of concrete petrographers. Different methods have been developed and implemented with varying degrees of success. To increase the reliability of estimated w/cm, the indentation hardness of laboratory prepared specimens of neat paste, mortar, and concrete was evaluated using a Buehler semi-automatic testing machine. Preliminary results indicate good correlations between the average indentation hardness measured on the Rockwell HRL scale and the w/cm of the specimens. The data demonstrate a potential for using these correlations to estimate the w/cm of hardened concrete. Testing protocols, sample preparation requirements, and the effects of aggregate and of the composition of concrete mixtures (portland cement and fly ash content) are illustrated. Directions for future work are also discussed.

The study of the stability of asphalt concrete mixture composition optimization mathematical models using imitative simulation

Abstract The method of statistical imitative simulation (Monte-Carlo) was used to simulate the heterogeneity of the produced asphalt concrete mixture (ACM) mineral part grading. The stability of optimisation of mathematical models of ACM composition developed by us was tested by a computer using tpe theory of this method application. Average values aij and their average standard deviations σ ij of seven (Aj = 7) finally hatched aggregate partial residues on control sieves i (i = 9) were set for research. Imported filler A 1 and reclaimed dust A 2 were replaced by their mixture Ā1 when the accepted ratio of these materials masses λ is 1, 2 and 3. The maximum (A max) and minimum (A j min) values of ACM materials quantity optimal composition were calculated from numerical values of aggregate with different heterogeneity ((minimum - σ ijmin, medium - σ ijvid , maximum - σ ijmax) increasing the number of computer imitations N (100, 300, 500, 1000, 5000, 10 000). The graphs of the difference between the calcula...

CONDITIONAL OPTIMIZATION MATHEMATICAL MODEL OF THE ASPHALT CONCRETE MIXTURE GRADING

A new partial conditional optimization method which enables to select the best ratio of imported fillers not only while designing the composition of asphalt concrete mixture but also while adjusting the composition of the produced asphalt concrete mixture according to the actual quality of hot fractions is presented. The constructed mathematical model, algorithm and the solved task prove that irrespective of the number of fillers (from 2 to 7 and more) the ratio of their mass can be selected which enables to produce an asphalt concrete mixture which meets the requirements of the composition project best. The mass ratio λ of imported fillers A 1 and reclaimed dust A 2, which settled and accumulated in the dry purification equipment of an asphalt concrete plant presented in Regulations DAT.AD-96 was taken into account for the first time. Methodological scientific novelty and a possibility to apply it in practice can improve the control of asphalt concrete mixture production.

THEORETICAL PRINCIPLES AND EXPERIMENTAL DATA TO IDENTIFY STABILITY OF ASPHALT CONCRETE COMPONENTS IN FINALLY DOSED MINERAL MATERIALS

The duration of asphalt concrete functioning depends on the quality of the asphalt concrete mixture used to pave the road. Grading of hot fractions sieved through technological sieves of asphalt concrete mixture, their pollution with particles of different size as well as stability influence on the quality of an asphalt concrete mixture. Each j - (j = 1...., m) aggregate mineral material or mixture is made up of two (mineral powder, particle of size less than 0,09 or 0,071 mm, and sand, particle of size from 2 to 0,09 mm or 5-0,071 mm) or three (crushed stone, particle size is larger than 2 or 5 mm) mineral components (i = 1, ..., k) . When required technological operations of asphalt concrete mixture production are carried out, the quantity and stability of any i - component in mineral materials change when they move through an asphalt concrete mixer. The more stable the quantity of mineral components in mineral materials (especially in finally dosed) is, the more uniform the composition of asphalt concrete mixture is produced. The experiments showed that when asphalt concrete mixture is produced applying a traditional technology in an asphalt concrete mixer of model D-597, D-508-2A, D-645-3 andD-590, sieved hot fractions of 0–5 mm and 5–15 are polluted with particles of different size by more than 10 per cent; and this pollution is neither uniform nor stable. Following a well-known theory, an average quadratic deviation σ of arithmetic undersized particles sieved through laboratory sieves ~aggregate mineral materials is the greatest when their mean X makes up 50 per cent; therefore, hot fractions of 0–5 mm and 5–15 mm were produced on the experimental data obtained from production as well as regression equations σ = ƒ( X )of statistical indeces of cold mineral powder. The values of average quadratic deviations σ µij of mineral component quantities in those finally dosed mineral materials are obtained from curves drawn according to the regression equations. They can be used to estimate dispersion σ2 Gi of mineral component i in asphalt concrete mixture which depends on the accuracy and stability of technological factors of an asphalt concrete mixer.

CONDITIONAL OPTIMIZATION MATHEMATICAL MODEL OF THE ASPHALT CONCRETE MIXTURE GRADING

A new partial conditional optimization method which enables to select the best ratio of imported fillers not only while designing the composition of asphalt concrete mixture but also while adjusting the composition of the produced asphalt concrete mixture according to the actual quality of hot fractions is presented. The constructed mathematical model, algorithm and the solved task prove that irrespective of the number of fillers (from 2 to 7 and more) the ratio of their mass can be selected which enables to produce an asphalt concrete mixture which meets the requirements of the composition project best. The mass ratio λ of imported fillers A 1 and reclaimed dust A 2, which settled and accumulated in the dry purification equipment of an asphalt concrete plant presented in Regulations DAT.AD-96 was taken into account for the first time. Methodological scientific novelty and a possibility to apply it in practice can improve the control of asphalt concrete mixture production. Frist Published Online: 30 Jul 2012

Ultrasonic Technique for Monitoring Concrete Strength Gain at Early Age

In this paper, the applicability of the wave reflection factor (WRF) technique for developing in-place procedures for assessing the rate of strength gain in concrete structures is determined. The research placed particular emphasis on highway pavement structures. Through a carefully planned experimental study involving laboratory-sized slab specimens of typical concrete mixture compositions used in highway/bridge construction, it is shown that the WRF technique accurately predicts the trends in strength development in such structures. The results appear promising in developing a predictive approach for strength gain based on the observed WRF trends.

High-Early-Strength-Concrete: Mix Proportioning with Processed Cellulose Fibers for Durability

The growth in fast-track construction and repair has prompted major efforts to develop high-early-strength (HES) concrete mixture compositions. Such mixtures rely on the use of relatively high cement and accelerator contents to increase the rate of strength development. These measures, however, seem to compromise the long-term performance of concrete in applications such as full-depth pavement patches. The hypothesis successfully validated in this research was that conventional methods of increasing the early-age strength of concrete involving the use of high-cement and accelerator contests increase the moisture and temperature movements, such as shrinkage, of concrete. Restraint of such movements in actual field conditions, by external or internal effects, generates tensile stresses that introduce microcracks and thus increase the permeability of concrete and accelerate various processes of concrete deterioration, including freeze-thaw attack. Fiber reinforcement of concrete is an effective approach to the control of microcrack and crack development under tensile stresses. Fibers, however, have not been known for accelerating strength development in concrete. The recently developed processed cellulose fibers were found to increase the early-age strength of concrete. This provides a unique opportunity to increase the rate of strength gain in concrete without increasing moisture and temperature movements, while actually controlling the processes of microcracking and cracking in concrete. Laboratory and preliminary outdoor test results confirmed the desirable resistance of processed cellulose fiber reinforced HES concrete to restrained shrinkage cracking, and thus, to different processes of deterioration under weathering effects. A field project involving fast-track full-depth patching with processed cellulose fiber reinforcement was implemented in Michigan.

Refractory lining of a furnace for pyrolysis of dichlorethane

Compositions of thermal-insulation concrete mixtures from which various elements of the lining of a furnace for pyrolysis of dichlorethane were produced have been developed. Burner blocks for the gas burners of the furnace were produced by vibrocasting. The refractories developed have provided reliable operation of the furnace, and for three years they have been in good condition.

Unfired refractory shapes based on chamotte-quartz binder compositions

Compositions of ceramic concrete mixtures based on chamotte-quartz binder compositions and a method of production of unfired especially complex shaped parts of these mixtures by vibrocasting have been developed.