Fresh and hardened properties of self-compacting concrete produced with manufactured sand

doi:10.1016/j.cemconcomp.2010.11.005

Cement and Concrete Composites

Volume 33, Issue 3, March 2011, Pages 353-358

https://doi.org/10.1016/j.cemconcomp.2010.11.005 Get rights and content

Abstract

Self-compacting concrete (SCC) is extensively applied in many construction projects due to its excellent fresh and hardened concrete properties. In recent years, manufactured sand (Msand) produced by crushing rock deposits is being identified as a suitable alternative source for river sand in concrete. The main objective of this study is to explore the possibility of using Msand in SCC. In this process, an attempt was made to understand the influence of paste volume and w/p ratio (water to powder ratio) on the properties of self-compacting concrete (SCC) using Msand. The powder and aggregate combinations were optimised by using the particle packing approach, which involves the selection of combinations having maximum packing density. The chemical admixtures (superplasticisers, viscosity modifying agent) were optimised based on simple empirical tests. Fresh concrete tests such as slump flow, T₅₀₀ and J-ring were performed on SCC; hardened concrete tests were limited to compressive strength. From the results, it was observed that relatively higher paste volume is essential to achieve the required flow for SCC using Msand, as compared to river sand. Low and medium strength (25–60 MPa) SCCs were achieved by using Msand based on the approach adopted in the study. Results showed that it is possible to successfully utilise manufactured sand in producing SCC.

Introduction

Self-compacting concrete (SCC) is a highly flowable concrete which does not segregate and can spread into place, fill the formwork with heavily congested reinforcement without any mechanical vibration [1]. In SCC, the aggregates contribute 60–70% of the total volume. Proper choice of aggregates has significant influence on the fresh and hardened properties of concrete [2]. Aggregate characteristics such as shape, texture and grading influence workability, finishability, bleeding, pumpability, segregation of fresh concrete and strength, stiffness, shrinkage, creep, density, permeability, and durability of hardened concrete [3]. The effects of shape and texture of fine aggregate are much more important than the effects of coarse aggregate [4].

River sand (Rsand) is being used as fine aggregate in concrete for centuries. However, increase in demand and depletion of river sand, along with restrictions imposed on the exploitation of the river sand, have resulted in search for a suitable alternative. From the literature [5], [6], [7], it was identified that the alternative materials for river sand include manufactured sand (Msand), industrial by products (some forms of slag, bottom ash), recycled aggregates, etc. Among these materials, Msand is receiving great attention these days as a replacement for river sand. The Msand is produced by crushing rock deposits to obtain a well graded fine aggregate which is generally more angular and has a rougher surface texture than naturally weathered sand particles. However, by using appropriate crushing technology (Impact crushing – Comminution in this type of crusher is the result of propelling particles with a rotor moving at high speeds, against an anvil or a curtain of falling particles), it is possible to produce cubical particle shapes with uniform grading, consistently under controlled conditions [8].

Manufactured sands contain high fines content [9]. Generally, the fines are composed of rock dust rather than the silts and clays in the case of natural sands. The maximum permissible limit of Msand fines (75 μm passing) as per ASTM C 33 is 7% [10] and the limit proposed for Msand fines (150 μm passing) as per the Indian standards is 20% [11]. Due to the presence of high fines content, the Msand has a significant influence on the water demand and the workability of the mortar [5]. The high fines content in crushed fine aggregate mainly increases the yield stress of the mortar due to increased interparticle friction, and contributes to the increase in plastic viscosity. The influence of fine aggregate on the properties of mortar to a large extent depends on the paste volume of the mortar. The negative effects of poorly graded and shaped aggregates can be eliminated or significantly reduced by increasing the volume of paste [12]. On the other hand, the mechanical and durability properties of the concrete are reported to be considerably improved by using Msand (especially produced from granite sources in comparison with the dolomite and sandstone origin) [5], [13]. For SCC, high powder (cement, cementitious materials and inert fillers) content is essential for achieving the required fresh concrete properties [14], [15]. Therefore, Msand, which contains large amount of fines, can be used as an alternative to river sand. The excess fines in Msand contribute to the filler content of the SCC. However, due to the higher water demand of Msand, the suitability for usage in SCC is questionable. While a number of studies have been conducted on the use Msand in conventional concrete, there are few instances of its application in SCC. The experimental investigations consisted of two phases. The first phase of the investigation involved the optimisation of the powder and aggregate combinations by using the particle packing concept. The degree of particle packing was measured in terms of packing density. Packing density is defined as the volume fraction of the system occupied by solids. Further, with the optimised combinations, experiments were conducted to evaluate the influence of paste volume and water to powder (w/p) ratio on the fresh and hardened properties of SCC by using Msand in the second phase.

Section snippets

Materials used

In the present investigation, Ordinary Portland Cement – 53 grade [16] and fly ash (Class F – from North Chennai Power Station, India), were used. The chemical composition and the physical properties of the cement and fly ash are given in Table 1, Table 2. Msand as fine aggregate (Source – Granite, Method of production – Impact crushing) and two different sizes of coarse aggregate (crushed granite – maximum sizes 12.5 mm and 20 mm) were also employed. The physical properties of aggregates are

Optimisation of paste composition

The powder (cement and fly ash) combination was selected based on the particle packing concept by using Puntke test [17]. The basic principle of the Puntke test is that the water which is added to the dry materials fills the voids in between the particles and acts as a lubricant to make the materials compact efficiently. The water, which is in excess after completely filling the voids, appears at the surface of the mixture, indicating the saturation limit. The combination of 60:40 (cement:fly

Fresh concrete properties

Experiments were conducted for possible combinations of the powder content (350–650 kg/m³) and the w/p ratio (0.7–1.5) with the optimised combination of aggregates (55:15:30) to investigate the influence on fresh and hardened concrete properties. The experiments were conducted with and without optimum VMA dosage. The optimum VMA dosage was used only for mixtures that segregated. As stated earlier, the particle size fraction finer than 125 μm of Msand is about 10 %, and these fines contribute to

Conclusions

The crushing processes of Msand affect the shape, grading of the Msand and the proportion of microfines (particles passing through 75 μm), particularly when compared to natural fine aggregates. These factors may affect the performance of the SCC. Therefore, appropriate crushing technology has to be selected to ensure that the Msand produced is having cubical shapes with uniform grading under controlled conditions.

The present investigation was conducted to explore the possibility of 100%

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Fresh and hardened properties of self-compacting concrete produced with manufactured sand

Abstract

Introduction

Section snippets

Materials used

Optimisation of paste composition

Fresh concrete properties

Conclusions

Cem Concr Res

Constr Build Mater

Cem Concr Compos

Cem Concr Res

Constr Build Mater

Self-consolidating concrete

Aggregates, concrete construction handbook

Aggregates in concrete

Effects of manufactured sand characteristics on water demand of mortar and concrete

Standard specification for concrete aggregates

Specification for coarse and fine aggregates from natural sources for concrete