Normal Weight Aggregate Research Articles

Lightweight Fly Ash-Plastic Aggregates in Concrete

The potential of using a synthetic lightweight aggregate (SLA) in concrete is examined. The aggregates are manufactured through thermal processing using plastic to encapsulate and bind fly ash particles. Nominal maximum-size aggregates of 9.5 mm were produced with fly ash contents of 0 percent, 35 percent, and 80 percent by total mass of the aggregate. The plastic used was high-density polyethylene, and the fly ash had a carbon content of 12 percent. An expanded clay lightweight aggregate and a normal-weight aggregate were used as comparison. Gradation, specific gravity, and absorption capacity are reported for the aggregates. Five batches of concrete were made with the different coarse aggregate types. Volume fractions of cement, water, fine aggregates, and coarse aggregates were kept the same for comparative purposes. Mechanical properties of the concrete determined included density, compressive strength, elastic modulus, splitting tensile strength, fracture toughness, and fracture energy. Salt-scaling resistance, a concrete durability property, was also examined. Compressive and tensile strengths were lower for the synthetic aggregates than for the normal-weight and expanded clay lightweight aggregates; however, comparable fracture properties were obtained. Relatively low compressive modulus of elasticity was found for concretes with the SLAs, although high ductility was also obtained. As fly ash content of the SLAs increased, all properties of the concrete were improved. Excellent salt-scaling resistance was obtained with the SLA containing 80 percent fly ash.

Manufacture of Concrete Test Panels and their Performance after Seven Years of Exposure in Arctic Marine Environment

In 1986, as part of CANMET's ongoing program to study the long-term durability of concrete in marine environment, 12 concrete panels, each 3.7 m long, were installed at a site at Nanisivik, Baffin Island, Northwest Territories, Canada. Six of the panels were made with normal-weight aggregate concrete, and the other six panels were made with concrete incorporating expanded shale lightweight aggregate. Other variables in the concrete mixtures included steel fibers and the replacement of portland cement by fly ash, slag, silica fume, or a combination of fly ash and silica fume. The cement replacement levels used ranged from 10% for silica fume to 50% for ground granulated blast-furnace slag. The water-cementitious materials ratio of all these concretes ranged from 0.37 to 0.49. The compressive and flexural strengths and modulus of elasticity were determined. The concrete panels were examined in 1989 after 3 years of exposure, and in 1993 after 7 years of exposure. Both the visual examination of the panels at Nanisivik and the microstructure examination of the cores taken from the panels indicate that, regardless of the type of concrete used, all the panels were in good to excellent condition after 7 years of very severe exposure, which included freezing and thawing cycling, ice abrasion, ice impact, and seawater attack.

INNOVATIONS FORUM : Self-Cured High Performance Concrete

Bad curing is often a source of later disease of a structure because of lower strength and higher permeability than anticipated. To overcome this problem, it has been suggested that concrete be cured directly where it is needed. To this aim a water reservoir was generated in lightweight aggregates (LWA) that were uniformly distributed in the concrete. Eleven mixtures were designed such that they should reach a minimum cube strength of 85 MPa irrespective of curing. The mixes contained 10-25% by volume lightweight expanded clay aggregates with respect to the total volume of aggregates. The aggregate size of LWA was varied between 4 mm and 8 mm. Results revealed that a partial replacement of normal weight aggregates by prewetted LWA leads to an internal water supply for continuous hydration of cement. Despite water loss by evaporation, there was a continuous strength gain: up to 25% more strength after one year compared with standard compressive testing after 28 days. Normal weight aggregate concrete reached considerably less strength at the same storage conditions. Application of such concrete in practice means that no curing from bad workmanship would not impair the concrete; in other words, it would be robust during construction.

Friction Angle Between Expanded Shale Aggregate and Construction Materials

Abstract Results of an experimental program are presented for the interface friction mobilized between expanded shale lightweight aggregate and commonly used structural materials: formed concrete, steel, and wood. A large-size direct shear device is used to perform tests. The mobilized friction between lightweight aggregate and solid surfaces of construction materials are compared with interface angles of friction associated with coarse normal-weight aggregates. The results provide useful design information on the appropriate mobilized angle of friction to be used while designing retaining structures with lightweight aggregate as backfill. The data are also useful in estimation of skin friction for piles driven through lightweight aggregate fills.

Drying of lightweight concrete produced from crushed expanded clay aggregates

When crushed lightweight aggregates are used in lightweight aggregate concretes very small water amounts evaporate from the concrete even in a dry environment. It is shown that a large portion of the free batch water is absorbed into the pore structure of the crushed aggregates. The relative humidity in concrete pore structure diminishes faster than in normal weight aggregate comparison concretes. Lightweight aggregate concrete is drying internally and therefore the structure thickness has a minor effect on concrete drying times. The exceptional drying properties of lightweight concretes produced from crushed aggregates enables a fast execution of the floor covering works without time consuming drying operations.

Estimating the elastic modulus of concrete made with artificially manufactured lightweight aggregates

Discusses the results of a study of the moduli of elasticity of concretes made with artificially manufactured lightweight aggregates subjected to uniaxial compression and uniaxial tension. Two artificially manufactured lightweight aggregates and one normal weight aggregate (for comparison) were used in the investigation. Concrete mixes designed to have compressive strengths varying from 20 MPa to 60 MPa were used in this study. Presents the results of static and dynamic moduli of elasticity, Poisson′s ratio, ultrasonic pulse velocity, compressive strength and tensile strength tests. Observes that the static modulus of elasticity in tension is nearly equal to the static modulus of elasticity in compression at a stress level of one‐third the ultimate stress. Compressive modulus values are shown to be dependent on the stress level and type of modulus, i.e. either secant or tangent. On the other hand, the tensile modulus is not affected by the stress level. The modulus of elasticity of lightweight aggregate concrete is about 60‐70 per cent of that of normal weight concrete. Compares the test results obtained in this study with research work carried out on other lightweight aggregate concretes by other investigators. Also presents the relationships between static modulus of elasticity, dynamic modulus of elasticity, compressive strength, and Poisson′s ratio, and equations for estimating elastic modulus and Poisson′s ratio.

Fatigue performance of normal weight and lightweight aggregate concrete beams reinforced with high tensile steel: Dave, N.J., Attisha, H.P. and Al Sanjari, K.A.A. Conf. Fatigue and Fracture in Steel and Concrete Structures, ISFF '91, Madras, India, Dec 1991 Vol 1 (Oxford & IBH Publishing Co. Pvt. Ltd, New Delhi, India, 1991) 627–636

The nonlinear vibration analysis of cracked structures could be a suitable indicator for diagnosing defects. When breathing cracks appear on the beam, its behavior can be modeled as a bilinear oscillator. In this paper, the nonlinear vibration behavior of a cantilever beam with multiple breathing cracks is investigated. For this purpose, the multi-cracked beam’s stiffness is calculated by introducing the effective length for the local stiffness reduction in the vicinity of cracks. Furthermore, owing to the importance of the damping variation in a cracked beam, its exact value is evaluated through theoretical expressions. A continuous polynomial function with the Weierstrass approximation is exploited to simulate the bilinear behavior of breathing cracks. By performing nonlinear analysis using the perturbation technique, the cracked beam’s dynamic behavior is studied. Moreover, the sensitivity of the response to the crack parameters in the primary resonance of the structure is analyzed. Finally, the sensitivity of the beam’s nonlinear response to the different number of breathing cracks and various crack depths is investigated. It is shown that the beam with a higher number of cracks or deeper ones has obvious softening behavior, and hence a more significant jumping can appear in the response.

Microstructure of the interfacial zone between lightweight aggregate and cement paste

Over recent years much attention has been given to the influence of the interfacial zone between aggregate and cement paste on the various properties of concrete. Most of the research work on this area has been carried out using normal weight aggregate. In the present paper experimental work on the interfacial zone between different types of lightweight aggregates and cement paste is presented. For high strength lightweight aggregate with a dense outer layer the nature of the interfacial zone between aggregate and cement paste is similar to that for normal weight aggregate. For lightweight aggregate with a weaker and more porous outer layer and for aggregate without any outer layer, the interfacial zone is more dense and homogeneous. Also for such aggregates the bond appears to be better due to an improved mechanical interlocking between the aggregate and the cement paste. The nature of the interfacial zone appears to depend on the microstructural characteristics of the aggregate.

Geotechnical Properties of Expanded Shale Lightweight Aggregate

Abstract In recent years lightweight aggregates are being used increasingly in geotechnical applications. This paper presents results of large-size one-dimensional compression and direct shear tests performed on lightweight aggregate. The compressibility and shear strength characteristics of the lightweight aggregate are compared with those of normal-weight aggregate using the same experimental setup. Results of the direct shear tests performed to determine the angle of friction between the geotextile and lightweight aggregate are also presented. In addition, static shear modulus values as determined from model pile tests are presented and compared with those reported for normal weight aggregates.

Water absorption by aggregates a simple approach to assessment of pore characteristics

Although the fundamental importance of pore structure of aggregates is recognised it is noted in the paper that successful linking of this with properties of concrete has not yet been possible. The authors accept that absorption of water by aggregates is important per se; it also allows indirect assessment of pore structure by characterising the pores, not in terms of sizes (based on assumptions about their shapes) but in terms of accessibility to water under simple immersion, low pressure (0.2 N/mm 2) and partial vacuum (630 mm Hg). Results are given for immersion periods from 20 seconds up to 2 years, for the first, and up to 90 days for the other two methods. The simple BS 812 technique used with normal weight aggregates is shown to be acceptable with the crushed limestone and with the five lightweight aggregates used. It is shown that the disturbance during mixing of ‘saturated’ high-porosity aggregates can lead to emission of significant volumes of water. The difference in behaviour between the sintered fly ash aggregate and the others is thought to be related to its more uniform and accessible pore structure arising from the fly ash particles and their sintering. It is concluded that useful information on aggregate pore characteristics is available from studies of simple water absorption tests.

Observations on the density and quality of concrete

Although fully compacted lower density concrete is made with lower density aggregates and, of necessity, these aggregates are of high porosity, this does not necessarily reduce the quality of the concrete. On the contrary, good quality structural concrete made with manufactured aggregates of relative density about 1.5, is at least as good as — and seems to be intrinsically better than — similar concrete made with normal weight aggregates. This results from the higher cement content and lower water-cement ratio used, from the lower E values of the aggregates, from the availability of water from aggregate pores and from the reduced tendency to cracking. Evidence is presented which suggests that in-situ lower density structural concrete has properties much closer to those assumed by the designer than is the case with normal weight concrete.

Model tests on peat — Geotextile — Lightweight aggregate system

Considerable research has been done in recent years dealing with the interaction of normal weight aggregate and geotextiles overlying soft compressible soils. In some instances, lightweight aggregate is used instead of normal weight aggregate to reduce settlements, and in the bridge abutment areas, to minimize lateral forces and to reduce drag loads on piles. However when used with geotextiles, it is not known whether the overall roadbed stiffness is affected when lightweight aggregate is used in place of normal weight fill. This paper reports the results of experimental research dealing with interaction of lightweight aggregate and geotextiles overlying peat subgrades. Variables investigated in the present study are: differing aggregate types and densities, thickness of the aggregate layer and geotextile types. The results indicate that the overall roadbed stiffness is unaffected when lightweight aggregate is used instead of normal weight aggregate, for small deflections and initial load application.

Guide for Use of Normal Weight Aggregates in Concrete

Guide for Use of Normal Weight Aggregates in Concrete

Early Strength Fly Ash Concrete for Structural Applications

Extensive data are presented on the properties, in the fresh and hardened state, of fly ash concrete containing normal weight and light weight aggregates suitable for structural applications. Tests on reinforced concrete beams and slabs are reported to show that fly ash concrete can exhibit structural performance similar to that of conventional concrete with adequate safety factors and predicted by existing codes.

Estimating long-term creep and shrinkage from short-term tests

Synopsis From experimental results on a range of mixes made with two lightweight and two normal-weight aggregates and from an analysis of numerous data of other investigators, it is proposed that creep and shrinkage at one year can be predicted from measured values at between 7 and 28 days by means of linear and power equations. Equations for the prediction of longer-term values are also given.

The proportion of protein from the normal and cataractous human lens which exists as high molecular weight aggregates in vitro

In the normal human lens high molecular weight aggregates (≥ 20 × 10 6 daltons) have been found to comprise only 3·1% of the total soluble protein and this percentage does not increase with age. In cataract the proportion is higher, representing 8·5% of the total soluble proteins, and much of it (5·1%) appears to be held together by disulphide bonds. These values are lower than those reported in the literature and do not support the suggestion that aggregation of human lens protein could be a cause of cataract.

Shear Strength of Stud Connectors in Lightweight and Normal-Weight Concrete

Steel-concrete composite construction using normal weight concrete has been used since early in the 1920s. Substantial use of composite construction began mainly for bridge structures in the 1950s as a result of the work done by Viest. Its primary growth in building construction during the last decade was a result of the simplified design provisions introduced into the 1961 AISC Specification. The development of these provisions were based on studies reported by Slutter and Driscoll. This study summarizes the results of tests on 48 two-slab pushout specimens. The main purpose of the investigation was to evaluate the capacity and behavior of stud shear connectors embedded in lightweight concrete. Two different types of normal-weight aggregates and three types of lightweight aggregate were examined. The lightweight concretes were made with both lightweight coarse aggregate with natural sand and with lightweight fines.