Normal Weight Aggregate Concrete Research Articles

Monotonic and cyclic flexural tests on lightweight aggregate concrete beams

Abstract. The work is concerned with an investigation of the advantages stemming from the use of lightweight aggregate concrete in earthquake-resistant reinforced concrete construction. As the aseismic clauses of current codes make no reference to lightweight aggregate concrete beams made of lightweight aggregate concrete but designed in accordance with the code specifications for normal weight aggregate concrete, together with beams made from the latter material, are tested under load mimicking seismic action. The results obtained show that beam behaviour is essentially independent of the design method adopted, with the use of lightweight aggregate concrete being found to slightly improve the post-peak structural behaviour. When considering the significant reduction in deadweight resulting from the use of lightweight aggregate concrete, the results demonstrate that the use of this material will lead to significant savings without compromising the structural performance requirements of current codes.

Permeability of Lightweight Aggregate Concrete with Mineral Admixture

This paper presents an experimental study on the permeability and the pore structure of lightweight concrete with fly ash, zeolite powder, or silica fume, in comparison to that of normal weight aggregate concrete. The results showed that the mineral admixtures can improve the anti-permeability performance of lightweight aggregate concrete, and mixed with compound mineral admixtures further more. The resistance to chloride-ion permeability of light weight concrete was higher than that of At the same strength grade, the anti-permeability performance of lightweight aggregate concrete is better than that of normal weight aggregate concrete. The anti-permeability performance of LC40 was similar to that of C60. Mineral admixtures can obviously improve the pore structure of lightweight aggregate concrete, the total porosity reduced while the pore size decreased.

An Investigation on the Interfacial Transition Zone of Lightweight Aggregate Concrete

The technique of linking the SEM photographs taken around the interfacial transition zone area is applied to observe the development of hydration products for lightweight aggregate and paste at the different curing ages. This research first determines the mixture proportions of the two types of concrete specimens with different aggregate unit weights. The lightweight aggregate used is the sludge kilned aggregate from Shihmen reservoir. The very small SEM samples to be observed are taken from the concrete compressive test specimens and must include both aggregate and paste. The research then observes the hydration products (such as CH, C-S-H) of calcium ion and the pozzolanic reaction on the samples. Finally it assesses if the aggregate will produce ion exchange with cement and generate the hydration products. The hydration products on either side of the interface with a range of 100μm are observed using 2000x magnification. From the results, it is found that (1) the development of hydration products of the lightweight aggregate concrete is similar to that of the normal-weight aggregate concrete, (2) the failure at the 91 days age is that the lightweight aggregate is sheared, (3) the bond stress of aggregate and paste is controlled by hydration products of paste, (4) the aggregate has not interacted with cement paste to produce hydration products, and (5) the development of hydration products proves that the amount of binder used in the concrete specimen will affects its compressive strength.

Effect of shale ceramsite type on the tensile creep of lightweight aggregate concrete

High water absorption ceramsite (YAS), low water absorption ceramsite (YCS), and normal-weight coarse aggregate (NCA) were used as coarse aggregates in concrete. YCS, YAS and NCA were respectively pre-soaked for 24h before their mixing into concrete. The net water/cement ratio of concrete with YCS, YAS and NCA was taken as 0.35. Mechanical properties and autogenous shrinkage of concrete made with the abovementioned coarse aggregates were determined. The tensile creep of these concrete was investigated by using a newly developed shrinkage-restrained testing ring. This study shows that the lightweight coarse aggregate concrete (LWAC) with YAS has the lower tensile creep than the LWAC with YCS, which has the similar tensile creep to the normal-weight coarse aggregate concrete (NC) with NCA.

Behavior of Channel Shear Connectors in Normal and Light Weight Aggregate Concrete (Experimental and Analytical Study)

This paper describes five push-out tests carried out at the University of Malaya using channel shear connector. The tests study experimentally and analytically, the behavior of channel shear connectors embedded in normal and light weight aggregate concrete (LWAC). Limited push-out tests are used to measure the accuracy of a proposed nonlinear finite element model for typical push-out test specimens. Using this model, an extensive parametric study performed to arrive at prediction for shear capacity of channel connectors in LWAC. An equation is suggested for the shear capacity of these connectors in LWAC.

Water absorption, permeability, and resistance to chloride-ion penetration of lightweight aggregate concrete

This paper presents an experimental study to evaluate effect of cumulative lightweight aggregate (LWA) content (including lightweight sand) in concrete [water/cement ratio ( w/ c) = 0.38] on its water absorption, water permeability, and resistance to chloride-ion penetration. Rapid chloride penetrability test (ASTM C 1202), rapid migration test (NT Build 492), and salt ponding test (AASHTO T 259) were conducted to evaluate the concrete resistance to chloride-ion penetration. The results were compared with those of a cement paste and a control normal weight aggregate concrete (NWAC) with the same w/ c and a NWAC (w/ c = 0.54) with 28-day compressive strength similar to some of the lightweight aggregate concrete (LWAC). Results indicate that although the total charge passed, migration coefficient, and diffusion coefficient of the LWAC were not significantly different from those of NWAC with the same w/ c of 0.38, resistance of the LWAC to chloride penetration decreased with increase in the cumulative LWA content in the concretes. The water penetration depth under pressure and water sorptivity showed, in general, similar trends. The LWAC with only coarse LWA had similar water sorptivity, water permeability coefficient, and resistance to chloride-ion penetration compared to NWAC with similar w/ c. The LWAC had lower water sorptivity, water permeability and higher resistance to chloride-ion penetration than the NWAC with similar 28-day strength but higher w/ c. Both the NWAC and LWAC had lower sorptivity and higher resistance to chloride-ion penetration than the cement paste with similar w/ c.

Fly ash lightweight aggregates in high performance concrete

Lightweight aggregates have been manufactured by sintering fly ash and crushing the product into suitable sizes. These aggregates possess unique characteristics that make them suitable for high strength and high performance concrete. Concrete produced using these aggregates is around 22% lighter and at the same time 20% stronger than normal weight aggregate concrete. Drying shrinkage is around 33% less than that of normal weight concrete. Moreover, the aggregates possess high durability characteristics required in high performance structures. The importance of the new aggregates lies mostly in the fact that superior qualities are achieved without having to increase the cement content. Thus it is possible to reduce the amount of cement by as much as 20% without affecting the required strength. Weight reduction may reduce precast concrete transportation costs as well as provide slender and spacious construction. Utilising fly ash to produce quality aggregates should yield significant environmental benefits.

Failure of lightweight aggregate concrete-filled steel tubular columns

Tests on steel tubular columns of square, rectangular and circular section filled with normal and lightweight aggregate concrete were conducted to investigate the failure modes of such composite columns. Thirty-six full scale columns filled with lightweight and normal weight aggregate concrete, eighteen specimens for each, were tested under axial loads. Nine hollow steel sections of similar specimens were also tested and results were compared to those of filled sections. The test results were illustrated by a number of load-deflection and axial deformation curves. The results showed that both types of filled columns failed due to overall buckling, while hollow steel columns failed due to bulging at their ends (local buckling). According to the above-mentioned results, and due to low specific gravity and thermal conductivity of the lightweight concrete the further interest should be concentrated in replacing the normal concrete by the lightweight aggregate concrete.

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.