Effect Of Aggregate Type Research Articles

Alkali-aggregate behaviour of alkali-activated slag mortars: Effect of aggregate type

The alkali–silica reaction in waterglass-alkali-activated slag (waterglass-AAS) and ordinary Portland cement (OPC) mortars was evaluated using three types of (siliceous and calcareous) aggregates. The tests were conducted to the ASTM C1260-94 standard test method. The mortars were studied by volume stability, mechanical strength and Hg intrusion porosity. The ASR products were studied with XRD, FTIR and SEM/EDX techniques. According to the results obtained, under the test conditions applied in this study, waterglass-AAS mortars are stronger and more resistant to alkali-aggregate reactions than OPC mortars. When the mortars were made with a reactive siliceous aggregate, expansion was four times greater in the OPC than in the AAS material. When a reactive calcareous (dolomite) aggregate was used, no expansion was detected in any of the mortars after 14 days, although the characterization results showed that the dolomite had reacted and calcareous-alkali products (brucite) had in fact formed in both mortars. These reactive processes were more intense in OPC than in AAS mortars, probably due to the absence of portlandite in the latter. When the calcareous aggregate was non-reactive, no expansions were observed in any of the mortars, although a substantial rise was recorded in the mechanical strength of AAS mortars exposed to the most aggressive conditions (1 M NaOH and 80 °C).

Effect of aggregate type, gradation, and compaction level on thermal properties of hot-mix asphalts

This paper investigates the effects of mix design factors on the thermal properties of Superpave asphalt concrete. The thermal properties were measured using a guarded testing device (k-alpha device) developed recently at the University of New Brunswick. Two aggregate types, three gradations (determined by the material retained on a 4.75 mm sieve), and four compaction levels (at 35, 70, 100, and 160 gyrations) were investigated. The aggregate was 12.5 mm maximum nominal size with PG58-34 asphalt binder used for all mixes. The findings show that the thermal conductivity of the asphalt concrete ranged from 1.7 to 2.1 W/m·K. The specific heat capacity varied with the aggregate source and ranged from 940 to 2000 J/kg·K. The thermal diffusivity was found to vary with aggregate source. The aggregate type was found to have the most significant effect on the thermal properties. The compaction level had an effect but not a statistically significant one. The range of thermal properties determined in this paper is comparable to that found in the literature.Key words: thermal properties, asphalt concrete, pavement temperature prediction, heat conduction, transient state, thermal conductivity, thermal diffusivity, heat capacity.

Effect of Aggregate Type on Mechanical Behavior of Dam Concrete

Due to the practical difficulties in performing a full size specimen test, dam concrete is usually sieved to remove the aggregate larger than 40 mm (1.6 in) when tested, which is called sieved concrete. This paper reports on a study that examined the influence of surface roughness of aggregate via two types of aggregates on the mechanical and fracture properties for dam and sieved concretes. The authors used two types of aggregates by full size specimens of 450 x 450 x 900 mm (18 x 18 x 35 in.) for tension and 450 x 450 x 450 mm (18 x 18 x 18 in.) for compression and by standard size specimens 150 x 150 x 550 mm (6 x 6 x 22 in.) for tension and 150 x 150 x 150 mm (6 x 6 x 6 in.) for compression, respectively. The complete stress-strain responses both in tension and compression were acquired through a systematic experimental program. The authors propose models to estimate the basic mechanical properties and the fracture parameters of the concretes with specimen ages; they propose theoretical models for normalized axial stress-strain curve in compression and for normalized axial stress versus normalized maximum crack width curve in uniaxial tension. Results include: the strengths, modulus of elasticity, and fracture energy increase with specimen age; the specimen size and maximum aggregate diameter significantly affect the fracture energy, peak strain, and crack width of concretes in uniaxial tension; and the performance of concrete with crushed coarse aggregate is higher than that of concrete with natural coarse aggregate.

Effect of coarse aggregate size on interfacial cracking under uniaxial compression

The effects of aggregate type and size are important parameters in the formation of interfacial transition zone (ITZ) structure and subsequently in the failure process of concrete. The influence of surface, rigidity and size of aggregates and water/cement (w/c) ratio of the matrix on bond strength at the ITZ and the interrelationship between the bond and the matrix in the failure process of concrete under uniaxial compression were studied. For this purpose a series of experiments were designed and carried out on mortars (with two different w/c ratios) containing single spherical steel aggregates. The ITZ properties and the failure process of concrete were investigated by means of tensile and compressive strength, and stress–volumetric strain measurements. It was observed that the effect of aggregate properties (high modulus of elasticity, smooth surface texture and size) on the weakness of ITZ and the failure process of concrete are of paramount importance for low w/c ratio composites. The effect of reduced bond properties was reflected in lowered critical stress levels for the low w/c ratio composites with larger aggregates.

The effect of shale in quartzite aggregate on the creep and shrinkage of concrete—A comparison with RILEM model B3

This paper presents the results of an investigation into the effects of increasing shale content in nominally “quartzite” aggregates on the creep and shrinkage behaviour of concretes made with such aggregate. The investigation was prompted by concern because of the increasing presence of the weaker and poorly shaped shale particles appearing in the quartzite aggregates being used in the Gauteng region of South Africa. In this investigation, two strength grades of concrete were prepared using varying proportions of shale in the stone and sand fractions of the quartzite aggregates. A secondary outcome of this investigation was the opportunity to assess the effect of aggregate type on the prediction of concrete creep and shrinkage using Model B3.

Method To Evaluate Rigid-Pavement Joint Sealant Under Cyclic Shear and Constant Horizontal Deflections

In recent years, the need for sealants in rigid pavement joints has become debatable, partly because of the unpredictable field performance of joint sealants. This inability to predict sealant performance stems from the fact that there is no laboratory evaluation method that accurately simulates field traffic and environmental loading conditions. A laboratory testing method was developed to predict the performance of rigid-pavement joint sealants. A research team at Virginia Tech designed a fixture that allows the evaluation of joint sealants under cyclic shear and static horizontal deflections. Shear deflection simulates vehicular loading, and horizontal deflection simulates expansion and contraction of concrete slabs due to temperature variation. Concrete specimens were prepared at a typical water-to-cement ratio of 0.45. Two aggregate types were used in the concrete mixes to evaluate the effect of aggregate type on sealant performance. Two commercially available sealants were investigated in the study. Sealant performance was evaluated for different joint widths and joint expansion. Specimens were loaded cyclically to failure; a 20 percent cohesive or adhesive debonding was considered a failure. A limited number of specimens were exposed to freezing and thawing cycles. The study showed quantitatively the effects of joint width, joint expansion, concrete aggregate type, and freezing and thawing cycles on sealant performance. Statistical models were developed to predict the number of loading cycles to failure for each sealant.

Failure Mechanism of Concrete

Concrete is a composite, and its properties depend on the properties of the component phases and the interaction between them. It is known that the interfaces are the weakest link in concrete, playing a very important role in the process of failure. This process is strongly related with the characteristics of the aggregates (especially coarse aggregates) and with the relative differences in strength between matrix and inclusions. This paper analyzes the mechanical behavior of high strength and conventional concretes prepared with coarse aggregates having significant differences in strength, shape and surface texture, porosity and absorption, and interface bond strength. Two different gravels and two different crushed stones were used. Concrete mixtures with water/cement ratios of 0.30 and 0.50 were designed. The effects of aggregate type and strength level on concrete failure mechanism, including tensile and compressive strength, stiffness, energy of fracture, and crack pattern, are discussed.

Abrasion resistance of concrete as a two-phase composite material

In this paper, concrete is treated as a two-phase composite material to investigate its resistance to abrasion. A relation based on the mixtures rule is considered; this predicts the abrasion resistance of concrete from the abrasion resistances and volume fractions of the mortar and coarse aggregate phases. Evaluation of the results of test on composites with coarse aggregate volume fractions ranging from 0 to 0.40 showed good agreement to this relation. The effects of aggregate type and water—cement ratio on abrasion properties of the constituent phases of the composite are discussed. The relations between the abrasion depth of concrete with length of slide have indicated good agreement to the theory of abrasion offered for metals; and correlations with some other mechanical properties of concrete have been demonstrated.

EVALUATION OF THE WINDSOR PROBE TEST TO ASSESS IN SITU CONCRETE STRENGTH.

A comprehensive study on the use of the Windsor probe system to assess in situ strength of concrete is reported. The tests were carried out on slabs of normal weight and light-weight concrete, having a strength of 5-70 n/sq.mm up to about a year. The effect of aggregate type and aggregate size was also investigated. The results were related to pulse velocity, internal fracture and core tests. If the Windsor probe system is used to evaluate absolute values of in situ strength, separate calibration charts are necessary to account for type of concrete, size of aggregate, aggregate type and age. As a general method of non-destructive testing, the probe system estimated strength up to 28 days better than small diameter cores, while the latter estimated strength of old concrete better. In particular, the probe system appeared unable to identify low strength at one year. (Author/TRRL)

Closure to “ Characterization of Asphalt Emulsion Treated Bases ” by Michael S. Mamlouk and Leonard E. Wood (March, 1981)

A laboratory investigation was performed to characterize cold mixed asphalt emulsion treated bases. Indirect tension, resilient modulus, Hveen and water damage techniques were used in the mixture evaluation. The effects of aggregate type and gradation, added moisture content, asphalt emulsion content, and temperature were determined. The mixture was characterized at different curing conditions in the field. The effect of temperature on the tensile and resilient characteristics of the mixture is apparent. In addition, curing increases both the tensile strength and the resilient modulus of the mixture. Reasonable correlations are found between the indirect tensile test and the resilient modulus test results. Vacuum saturation has some effect on the tensile and the resilient properties of the mixture. Other asphalt emulsion mixture properties such as density, retained moisture content, and air voids are evaluated

Characterization of Asphalt Emulsion Treated Bases

A laboratory investigation was performed to characterize cold mixed asphalt emulsion treated bases. Indirect tension, resilient modulus, Hveen and water damage techniques were used in the mixture evaluation. The effects of aggregate type and gradation, added moisture content, asphalt emulsion content, and temperature were determined. The mixture was characterized at different curing conditions in the field. The effect of temperature on the tensile and resilient characteristics of the mixture is apparent. In addition, curing increases both the tensile strength and the resilient modulus of the mixture. Reasonable correlations are found between the indirect tensile test and the resilient modulus test results. Vacuum saturation has some effect on the tensile and the resilient properties of the mixture. Other asphalt emulsion mixture properties such as density, retained moisture content, and air voids are evaluated