Influence Of Lightweight Aggregate Research Articles

Influence of Lightweight Aggregates and Supplementary Cementitious Materials on the Properties of Lightweight Aggregate Concretes

Influence of Lightweight Aggregates and Supplementary Cementitious Materials on the Properties of Lightweight Aggregate Concretes

Mechanical properties of alkali-activated slag lightweight aggregate concrete

The mechanical properties of alkali-activated slag lightweight aggregate concrete (AAS-LWAC) were deep investigated. A total of 108 AAS-LWAC samples were prepared for compressive strength test, splitting tensile strength test, and flexural strength test. The microstructures of AAS-LWAC were characterised in depth using scanning electron microscopy (SEM). Compared with clay ceramsite and shale ceramsite as the lightweight aggregate (LWA), AAS-LWAC with fly ash ceramsite as the LWA exhibited the highest compressive strength. Besides, the compressive, splitting, and flexural strengths of AAS-LWAC decreased with increasing LWA content. Moreover, compared with polypropylene fibres and basalt fibres, steel fibres can significantly increase the compressive, splitting, and flexural strengths of AAS-LWAC, with an optimal volume content of 0.6% steel fibre. Furthermore, a modified formula for the variation in compressive strength of AAS-LWAC over time was proposed, considering the influence of LWA.

Experimental study on self compacting concrete using light weight aggregate

The inherent properties in Self Compacting Concrete (SCC) makes very popular in recent decades. When compaction of concrete is very difficult due to placing condition or congested reinforcement, SCC plays major role where it compacts by its own. This study investigates the influence of Light Weight Aggregates (LWA) in Self Compacting Concrete (SCC). Various tests are done such as workability, mechanical, and durability properties were determined and the results are discussed. To explore the possibility of using diatomite aggregate an attempt has been made by partially replacing natural coarse aggregate by diatomite aggregate with 5%, 10%, 15% and 20%. The results exhibited that replacement of natural coarse aggregate with diatomite aggregate has 22%, 24%, 26%, 28% decrease in compressive strength with replacement percentage of 5%, 10%, 15%, 20%.

Influence of lightweight aggregates on the physical and mechanical residual properties of concrete subjected to high temperatures

This research studies the high temperature behavior of lightweight aggregate concretes (LWAC) by providing a comprehensive study that regroups the physical, thermo-mechanical and mechanical properties of three different LWACs. Then these properties are compared to the properties of a normal-weight concrete (NWC) as well as to those of the mortar phase of these concretes, thus, enabling us to isolate and identify specific behaviors of the lightweight aggregates (LWA). Contrary to the normal weight aggregates, the LWAs showed a compatibility in thermal strain with the mortar phase, which led to fewer cracks in the interfacial transition zone (ITZ) and thus, it resulted in a divergence in behavior between LWACs and NWC, particularly for the residual permeability and tensile strength values. While LWACs generally exhibited lower decrease of failure strengths, and Young Modulus with temperature than NWCs, its Poisson’s ratio was greatly decreased after 300 °C.

The influence of lightweight aggregate, freezing–thawing procedure and air entraining agent on freezing–thawing damage

This article presents the results of a study dealing with the concrete resistance to repeated cycles of freezing and thawing of nonair entrained, fine lightweight aggregate (LWA) and air‐entrained concrete when tested in accordance with ASTM C 666, procedures A and B. The water‐to‐binder ratios (w/b) of the mixtures ranged from 0.25 to 0.35, and the percentage of cement replacement by silica fume were 7% on a weight basis and constant throughout study. Binder dosage was 500 kg/m3 and constant. LWA was pumice aggregate (PA) and expanded perlite aggregate (EPA). PA and EPA were replaced by 10, 20, and 30% of total volume of 1 m3 as a fine aggregate (0–2 mm fine aggregate fraction). Also one group was produced with air entraining agent by 0.1% ratio of binder dosage. The 200 freeze–thaw cycles were carried out according to ASTM C666/C666M‐15, procedure A and B. The compressive strength, ultrasonic pulse velocity, relative dynamic modulus of elasticity and dry unit weight of mixtures were investigated. Based upon the analysis of the test data, it is concluded that samples contain air‐entrained agent and 10% LWA were more durable than that of control sample. With the increasing of the LWA content the freeze–thaw resistance of samples decreased. Thus, higher content of LWA is not recommended when it is to be subjected to repeated freeze–thaw cycles. Freezing–thawing procedures were compared with each other and found that procedure A was more severe than procedure B.

Ammonia Nitrogen Transformations in a Reactor with Aggregate made of Sewage Sludge Combustion Fly Ash.

The influence of light weight aggregate made of fly ash from sewage sludge thermal treatment (FASSTT LWA) on ammonia nitrogen metabolism, and on quantitative and qualitative changes of microorganisms colonizing the filling, was investigated. Two reactors were used in the experiment. The first was filled with gravel, the other with FASSTT LWA. The reactors were operated with a wastewater hydraulic loading rate of 5 mm(3) mm(-2) d(-1). During the eleven-week experiment, high efficiency of ammonia removal was observed. The lower concentrations of nitrites and nitrates in the effluent indicate that ammonia nitrogen removal resulted not just from nitrification. Nitrate concentration increase was reflected in a decrease in nitrogen removal efficiency. One possible explanation for this phenomenon is that in the period when ammonia nitrogen and nitrites were present in the reactor's FASSTT LWA filling, facilitating conditions occurred for the deammonification process.

Influence of lightweight aggregate on the bond properties of concrete with various strength grades

This paper presents the comparison of the bond and mechanical properties of lightweight oil palm shell concrete (OPSC) and normal weight concrete (NWC) with three different strength grades of 25, 35 and 45MPa. Although the mechanical properties such as splitting tensile strength and modulus of elasticity as well as the performance of drying shrinkage of OPSC were found to be inferior compared to NWC, the bond strength of OPSC was found to be up to 80% higher compared to the corresponding NWC of equivalent cube compressive strength grade. Results also showed that the shape of the bond stress–slip curve for OPSC was similar to conventional NWC. In addition, in this paper, modified bond models based on the CEB–FIP bond model was proposed for both OPSC and NWC which were found to give good prediction of the experimental bond stress–slip curve of the concretes.

Influence mechanism of lightweight aggregate on concrete impermeability: prediction by ANN

The influence of lightweight aggregate (LWA) on concrete impermeability is complex, varying according to LWA type, water–cement ratio and curing age. A convenient, quick method to predict impermeability of lightweight concrete is needed. To investigate the influencing mechanism, the microstructure of LWA and the interfacial transition zone are observed, and the water absorbing/releasing character of LWA in cement paste is studied. Chloride diffusion coefficients of concrete with different LWAs and water–cement ratios are also tested at different ages. LWA is found to have both an advantageous and disadvantageous influence on concrete impermeability. Based on 108 experimental datasets collected, an artificial neural network (ANN) model is applied to predict the influence of LWA on chloride diffusivity of concrete. The model is developed, trained and tested using a multi-layer back-propagation method. The predicted values are then compared with actual test results; the average relative error of prediction is found to be 4·14% and coefficient of determination (R2) is 0·97. These results indicate that the developed model has successfully learned the relationship between the different input and output parameters, and can predict the chloride diffusivity with accuracy adequate for practical design purposes. The ANN procedure provides guidelines to select the appropriate LWA for the required chloride diffusivity of concrete, reducing trial and error attempts, and saving both cost and time.

Practical Approach for Assessing Lightweight Aggregate Potential for Concrete Performance

The properties and amount of lightweight aggregates used in a concrete mixture can significantly influence its mechanical properties and density. Nevertheless, such influence cannot be accurately described and used in practical application without an extensive experimental work. A practical evaluation method for assessing the influence of lightweight aggregate on concrete properties is required to anticipate the performance of concrete in advance and chose the most suitable lightweight aggregate for a certain structural application. In this paper, existing models are reviewed, generalized, and validated to obtain a methodology for assessing the potential of the lightweight aggregates to provide a specified concrete density, modulus of elasticity, and compressive strength. A practical evaluation methodology is proposed and validated with four different lightweight aggregates, obtaining correlations between measured and estimated density; modulus of elasticity; and compressive strength of 93.4, 84.8, and 91.7%, respectively. Therefore, this methodology allows practical and reliable comparison and selection of lightweight aggregates based on only one trial mixture.

Influence of Lightweight Aggregates and GRP By-Product Powders on the Properties of Self-Compacting Concretes

Self-compacting lightweight concrete was developed to attain good workability, high compressive strength (at least 50 MPa), minimum cracks, and low specific weight (less than 2000 kg/m3), as well as low elastic modulus (about 30 GPa). The attention was also focused on sustainability of this construction material, which was improved by using in the mixture both GRP industrial by-product as filler and artificial (light expanded clay) or recycled (demolished concrete) as coarse aggregates replacing natural gravel. Satisfactory, if not excellent, results were obtained from the collected experimental data.

Nitrogen removal from wastewater in vertical flow constructed wetlands containing LWA/gravel layers and reed vegetation

The influence of light weight aggregates made of fly ash from sewage sludge thermal treatment (FASSTT LWA) on the nitrogen removal efficiency from artificial wastewater in constructed wetlands (CW) with vertical flow reed bed was investigated. Thirty lysimeters with six different double-layer bed constructions (upper layer of FASSTT LWA with thicknesses of: 0 cm, 12 cm, 25 cm, 50 cm, and 100 cm of the total depth of the lysimeter, above a lower gravel layer), either with or without reed plants were operated with wastewater hydraulic loading rate of 4.67 mm/d. During a six-month experiment, high efficiency of ammonia removal was observed. The influence of FASSTT LWA as a bed material and the presence of reed on CW treatment efficiency was determined. The highest total nitrogen removal efficiency, 59.5%, was obtained in the CW with double-layer lysimeters consisting of 25% FASSTT LWA (upper layer), and 75% gravel (lower layer), and planted with reed.

Effect of lightweight aggregate pre-wetting on microstructure and permeability of mixed aggregate concrete

The influence of lightweight aggregate (LWA) pre-wetting on the chemical bound water and pore structure of the paste around aggregate as well as concrete permeability were investigated. The results show that, in early age the dry LWA has significant effect on the formation of dense paste around it and improving the concrete impermeability. However the prewetted LWA has strong water-releasing effect in later age, which increases the hydration degree of the paste around it, and makes the adjacent paste develop a structure with low porosity and finer aperture, furthermore the concrete impermeability can be improved. It is suggested that, as for concrete with low durability requirement, the LWA without pre-wetting treatment can be used as long as meet the workability requirement of fresh concrete, the good impermeability of concrete can be gained as well. As for concrete with high durability requirement, the prewetted LWA should be used, and the pre-wetting time should be extended as long as possible, in order to optimize the concrete structure in long term, and improve the concrete durability.

The influence of lightweight aggregate on the physico-mechanical properties of concrete exposed to freeze–thaw cycles

A laboratory investigation was carried out in order to evaluate the quality of concrete with 10%, 20% and 30% combination of pumice aggregate and expanded perlite aggregate instead of fine aggregate (0–2 mm), and 0.1% air-entraining agent ratio. Several properties related to durability were determined, and particular attention was put on the resistance of the concrete mixes to the freezing and thawing cycles based on ASTM C 666, procedure B. Compressive strength and unit weight of concrete were decreased with increase of LWA but water absorption and sorptivity coefficient of concrete were increased before and after 100 freeze–thaw cycles. After 100 cycles of freeze–thaw 10% pumice aggregate and expanded perlite aggregate increased compressive strength of samples 3 and 4% respectively when compared to control samples. Reduction in the compressive strength due to the air-entraining agent was around 9% after 100 freeze–thaw cycles.

Influence of Lightweight Aggregate on Durability of High Performance Concrete

High performance concrete (HPC) with a water/cement ratio (w/c) of 0.32 and different lightweight aggregate (LWA) contents (0%, 25%, 50%, 75%, 100%) were prepared, and the influence of LWA on concrete frost-resistance and impermeability at different ages were studied, as well as the hydration degree, hydrated product, pattern and pore structure of the paste around aggregate. The results show that, by replacing normal weight aggregate (NWA) with 50% and 100% volume contents of pre-wetted LWA respectively, the chemical bound water of the cement paste surrounding aggregate are increased 12.1% and 22.7% as compared to concrete mixed without LWA. And at 28 days, lightweight aggregate concrete has the highest Ca(OH)2 content, whereas the 90-day Ca(OH)2 content of normal weight concrete is the highest. This proves that, with the increase of LWA content in concrete, both of the internal curing effect of pre-wetted LWA and secondary hydration effect of fly ash (FA) are strengthened, this can also be verified by the SEM study. Furthermore, the pore structure of the cement paste around aggregate can be improved consequently. The performance of frost-resistance of HPC can be improved by mixing LWA, the 90 day-frost-resistance of lightweight aggregate concrete is about 2.5 times of that of concrete mixed without LWA. The influence of LWA on the impermeability of HPC is different from normal concrete. When LWA content is more than 50%, the HPC impermeability decreased obviously, however at later age the difference between them becomes minor.

Influence of lightweight aggregate on the microstructure and durability of mortar

The results of an investigation on the effect of dry and prewetted lightweight aggregates on the microstructure and durability of mortar are presented in this paper. The results are compared with those obtained for normal aggregate mortar. There appears to be only a small difference in the microstructure of the interfacial transition zone (ITZ) between dry and prewetted lightweight aggregate mortars. The porous ITZ surrounding lightweight aggregate appears to extend for about 10 and 15 μm from the aggregate surface for dry and prewetted lightweight aggregates, respectively. The ITZ for dry and prewetted lightweight aggregates seems to be surrounded by dense paste that extends from 10 to about 50 μm from the aggregate surface. This dense paste has lower porosity than that observed in the bulk paste located 50 μm and farther from aggregate surface. The normal aggregate mortar prepared with the same water/cement ratio appears to have porous ITZ that extends beyond 35 μm from the aggregate surface. The dry and prewetted lightweight aggregate mortars seem to have a lower sorptivity and electrical conductivity than does the normal aggregate mortar. Lightweight aggregate mortars also appear to have excellent resistance to sulfate attack as compared with normal aggregate mortar.

Influence of lightweight aggregates on thermal strain capacity on concrete

Synopsis The tensile strain capacities of concretes with densities between 1200 and 2300 kg/m3 are determined by means of a short-term stressing technique. The thermal strain capacity of lightweight aggregate concrete is up to 2½ times greater than that of flint gravel concrete of similar workability and strength. Lightweight aggregate concretes also have lower coeficients of thermal expansion and reach slightly higher maximum temperatures due to hydration. It is demonstrated that the main influencing parameter on tensile strain capacity is the strengthlelastic modulus ratio.