Manjunath M, Research scholar, Walchand College of Engineering, Sangli, and Prakash K B, Principal, Government Engineering College, Haveri

This paper presents an experimental investigation on the effect of alternate wetting and drying on recycled aggregate concrete with different supplementary cementitious materials (SCM). The supplementary cementitious materials considered in the present study include fly ash, silica fume and ground granulated blast furnace slag used as a partial replacement of cement. The compressive strength of concrete subjected to 45 cycles of alternate wetting and drying is determined for the various%age replacements of natural coarse aggregates by recycled aggregates.Test results indicate that the durability aspects of recycled aggregate concrete as evaluated by alternate wetting and drying test can be improved through the use of SCM admixtures.

Introduction

The utilization of the recycled aggregates created from processing construction and demolition waste in new construction has become more important over the last two decades. There are many factors contributing to this, from the non-availability of new material and the damage caused by the quarrying of natural aggregate and the increased disposal costs of waste materials. Construction and demolition waste are generated mainly from demolished concrete and masonry structures. Due to advances in manufacturing of crushing machinery and recycling processes, it became possible to scale or crush down large masses of construction and demolition waste into smaller particles to produce recycled aggregate at acceptable cost.

Recycling of concrete waste is necessary from the viewpoint of environmental preservation and effective utilisation of resources. The utilization of recycled concrete aggregates is particularly very promising as 60-80% of concrete is made of aggregates [3].

A review of several early studies indicated that, compared with concrete mixtures containing natural aggregate, the mixture containing recycled-concrete aggregate generally gave at least two-thirds of the compressive strength and modulus of elasticity, and show satisfactory workability and durability [5]. In general, the effects of using recycled-concrete aggregate instead of natural aggregate are (a) reduced compressive strength (b) reduced modulus of elasticity (c) increased drying shrinkage and creep and (d) increased damping capacity. The reduction in strength ranges between 12 to 25%, while, the reduction in modulus of elasticity varies from 10 to 33%. Creep of recycled aggregate concrete is found to be 30 to 60% greater and drying shrinkage 20 to 50% greater than concrete made with natural aggregates [7 & 1].

Recycled aggregates are composed of the original aggregates and the adhered mortar. It is well known that physical properties of recycled aggregates are very much dependent on the type and quality of the adhered mortar. The adhered mortar is a porous material; its porosity depends upon the water-cement ratio of the recycled concrete employed [4].

As the adhered mortar is often prone to attract more water than the original aggregate, the absorption capacity of recycled aggregates is known to be greater than that of natural aggregate; this is believed to be one of the most significant factors affecting the recycled aggregate concrete. Although there is no clear-cut relation between the strength of concrete and the water absorption of aggregate used, the pores at the surface of the particle affect the bond between the aggregate and the cement paste, and may thus exert some influence on the strength of concrete [6].

When the aggregate to be used is limiting the strength of concrete, the overall performance is usually affected; in this case, the obvious solution is to improve the performance of the aggregate and other concrete components. The factors that contribute to increased strength and performance include use of supplementary cementitious materials and chemical admixtures [2].

Durability of concrete is defined as its ability to resist weathering action, chemical attack, abrasion, or any other process of deterioration. Water, which is the primary agent of both creation and destruction of many natural materials, happens to be central to most durability problems in concrete. In porous solids, water is known to be the cause of many types of physical processes of degradation. The movement of the various fluids through concrete takes place not only by flow through the porous system but also by diffusion and sorption [5].

An exposure condition which cannot be avoided, is the exposure of mature concrete to alternating wetting and drying – a temperature cycle frequently met with in nature. Alternating wetting and drying represents much more severe conditions because a build-up of salts within the concrete can occur in consequence of the ingress of water, followed by evaporation of pure water, with the salts left behind [6].

For concrete produced with recycled aggregates, the volume of pore space in concrete, as distinct from the ease with which a fluid can penetrate it, is measured by absorption, thus testing of concrete subjected to alternating wetting and drying cycles serves as a measure of durability index.

Main objective of this experimentation is to study the effect of alternate wetting and drying on concrete produced by replacing natural coarse aggregates by recycled aggregates and on recycled aggregate concrete with different supplementary cementitious materials. The grade of concrete adopted is M20, as it is the widely used structural concrete. Three supplementary cementitious materials (SCM) considered for the study are fly ash (FA), ground granulated blast furnace slag (GGBS) and silica fume (SF). Each of the mineral admixture is used independently in the recycled aggregate concrete. The different%age replacement of natural coarse aggregates by recycled aggregates considered are 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100%. The compressive strength of concrete subjected to 45 cycles of alternate wetting and drying is determined.

This section of the article is only available for our subscribers. Please click here to subscribe to a subscription plan to view this part of the article.

Click Here
To Know More or to Contact the Manufacturer
Please let us know your name.
Invalid Input
Please let us know your Designation.
Please let us know your Contact Number.
Please let us know your email address.
Please brief your query.
Our other Value-Added Services:

To receive updates through e-mail on Products, New Technologies & Equipment, please select the Product Category(s) you are interested in and click 'Submit'. This will help you save time plus you will get the best price quotations from many manufacturers, which you can then evaluate and negotiate.

Invalid Input
Invalid Input
Invalid Input
Samir Surlaker, Director, Assess Build Chem Private Limited, emphasizes the importance of a clear cover for a concrete structure since concrete as a porous material needs protection of its reinforcement. Along with the thickness (quantity) of cover, the porosity of

Read more ...

Concrete technology has come a long way since the Romans discovered the material, with a number of ingredients, which include a host of mineral and chemical admixtures, besides of course, the Portland cement, aggregates (coarse and fine), and water. These ingredients

Read more ...

Anil Kumar Pillai, GM, Ramco Cements, discusses two major softwares (Life 365 and DuraCrete), used in the industry for protection of RCC structures. The common design approach is faulty because we consider only the loading aspect, whereas the environmental aspect is equally

Read more ...

Fibre Tuff, macro synthetic polypropylene fibres, are heavy-duty synthetic fibres that are specially engineered for use as secondary reinforcements, providing excellent resistance to the post cracking capacity of concrete. They are replacing steel fibres in a range

Read more ...

Reinforced concrete design and construction practice has historically focused on the use of bonded straight or bend rebar as a method for rebar anchorage. This relies on bond integrity between the rebar and the concrete so that sufficient anchorage

Read more ...

Innovation and entrepreneurship are essential ingredients in building a successful commercial venture. The ways in which these two concepts fuel enterprise are something entrepreneur's never stop exploring. There is no doubt that innovation were

Read more ...

Alite and belite are the predominant phases of Portland cement formulation. Alite is impure tricalcium silicate (C3S) and belite is impure dicalcium silicate (C2S). The impurities are an integral part as cement is manufactured

Read more ...

Concrete is a versatile construction material and day by day its consumption is increasing globally. It is second only to water in the global consumption. No civil engineering structure is feasible without using concrete

Read more ...

The use of Graphene with concrete has been talked about and researched ever since Graphene was invented in 2010 which grabbed its inventors a Nobel prize. Nanospan is the first company in the world to break technological and commercial

Read more ...

Fosroc is the foundation of the JMH Group. It employs over 1700 employees in 17 operating companies based in Europe, the Gulf & Middle East, India, South Asia, and China. Through FGT, its trading company, it services another 50 countries

Read more ...

Established in 1983 by French expatriate entrepreneurs, the Dextra Group has a long history of growth and development, driven by strong entrepreneurship and innovation. It has diversified into three main activities: manufacturing, trading and freight forwarding

Read more ...

Jyotirmoy Mishra, Ph.D. Scholar, Department of Civil Engineering, Veer Surendra Sai University of Technology, Burla, Odisha, presents his research on the feasibility and compressive strength performance of geopolymer concrete

Read more ...

As every one ton of Cement (OPC) produced, emits 0.96 tons of CO2, there is an urgent need to promote blending materials (ex. GGBS &PSC) and screened slag, to achieve lower CO2 emissions, reduce greenhouse gas effect, reduce exploitation

Read more ...

In most of the developing countries, demand for steel for use as a reinforcing material is increasing day by day. However, when steel is in short supply, one can consider bamboo as an alternative material for reinforcement

Read more ...

There is high demand for white cement in countries with hot climates, as more heat is reflected from white concrete surfaces as compared to standard grey concrete. As a value-added product, white cement is becoming

Read more ...

Garry Martin, Director - Major Projects, Low & Bonar Construction Fibres, presents a new examination of the benefits of micro fibres in both the plastic and hardened state of concrete and their contribution to increased sustainability.

Read more ...

An integrated material and structural design strategy of strength through durability is the need of the hour since structures are designed for ductility and structural integrity. Dr. S. B. Hegde, President – Manufacturing

Read more ...

The demand for structural strengthening of ageing structures is growing rapidly in buildings, industrial structures, infrastructure projects like bridges, dams, etc. Structural Strengthening also

Read more ...

Durability and strength are two most important criteria and requirements for the long-term performance of concrete structures against weathering action, chemical attack and abrasion. Any deficiency

Read more ...

Cement is a key binder component of concrete production in the building industry. It is a complex hydraulic binder, made up of four main clinker components; alite (Ca3SiO5), belite (Ca2SiO4)

Read more ...

×
Sign-up for Free Subscription
'India Construction Week'
Weekly e-Newsletter on Construction Industry
Get the latest news, product launches, projects announced / awarded, government policies, investments, and expert views.
Click here to subscribe.