Causes of Deterioration for Concrete and Masonry Structures and Repair and Rehabilitation Techniques

    Prof. K. Ganesh Babu, (Former Director, CBRI, Roorkee) Department of Ocean Engineering, IIT Madras, Chennai.

    The inadequate performance of constructed facilities is a cause for concern even for the most advanced of the nations in the world. The losses in downtime in itself, without even considering the effects of failures, are being estimated to be a fair percentage of the gross national product of any nation. The main causes have been attributed to the reasons ranging from improper materials of construction, construction procedures, and inadequate maintenance apart from the casual attitude to repair and rehabilitation. The paper attempts to focus the attention on some of these aspects in the construction scenario in a brief way.

    The paper also presents a brief review of the various aspects related to the parameters influencing the repair and rehabilitation strategies for addressing the deterioration of concrete and masonry structures in the increasingly aggressive environments of the present day. These parameters can be broadly classified into two major sections, environmental parameters and material parameters, with the material parameters including both that are relevant to the concrete or mortar and the steel in it. The primary parameter that influences the deterioration of both concrete and masonry is simply the porosity of these materials that allows the permeation of the aggressive environment into it over a period of time. The characteristic that influences the time to initiation of corrosion initially and later the cracking of concrete is also the porosity. The reinforcement is generally in a passive state up to initiation of corrosion and after initiation, it is influenced by the environment in concrete up to cracking and later by the environment itself. The broad relationships between these and repair strategies have also been discussed along with their effectiveness.

    Introduction

    In the larger canvas of the construction scenario, the need for speedy, efficient, safe and economical (affordable) construction practices, be it through materials, design or engineering and technology in construction practices, is very important. The heavy and large volume needs of the present day have made the planning, construction, maintenance and rehabilitation of structures an essential part of the modern economy. Apart from this, the major industrial needs for water and transport have given a boost to the various coastal habitats that need to perform in the most severe natural environments throughout their entire lifetime.

    Concrete, as a material of construction even for structures situated in these severe environmental conditions of the oceans, has been accepted for a long time. It is popularly believed that concrete structures are designed for a maintenance free operating life of well over fifty years. However, the experience in the recent past show that there have been a number of cases of severe damage or even failure in some cases, within a very short span. There have been a large number of investigations on the problems of the deterioration of concrete and the corrosion of steel in concrete in different environmental conditions. A comprehensive review of all these works and the ones related is almost too much even to attempt. However, a proper understanding of at least the significant parameters that influence the behaviour of concrete and steel in concrete is very much essential to ensure a satisfactory repair and rehabilitation strategy.

    Planning and Design

    Major constructed facilities assume immense significance, as these are the commercial hubs that need to serve the multi-faceted requirements of the industry and the nation. Other structures more often evolve out of the specific needs of a particular use. The requirements of such facilities will need a critical understanding. Apart from these, the specific yet sporadic requirements of some of the industries can only be looked at on a case to case basis.

    While the choice and planning of any specific structure may be a matter of concern, a detailed discussion of the design of these facilities is not really a matter for huge concern, in most cases. One may have to have an understanding of the forces and their estimation and the corresponding requirements from the structures to withstand these loadings, and some of the prominent ones may be listed as - Wind forces, Dead and live loads, Dynamic and impact loads, Earth and hydrostatic pressure, and also Secondary loads during erection.

    These do not include the specific and explicit evaluation of the forces from natural calamities like earthquakes, landslides tsunami etc. Also it is possible to adopt several combinations of the above if one has the requirements and possibilities appropriately documented. The present scenario in most cases is that the choice is based on tradition rather than effectiveness. The excessive dependence on the available codal provisions limits the vision and ingenuity of several progressive organizations.

    Construction and Maintenance

    While one can easily understand the fact that, with a proper assessment of the requirements and forces the design can result in a fairly lasting structure, though the construction quality assurance is often neglected inadvertently. In recent years, the procedure of ensuring quality through supervision consultants or even third party QA/QC, has not been very successful. This is because of the fact that the construction tender document is taken to be the final authority and any modifications or exceptions even if necessitated at a later stage cannot easily be incorporated.

    The International recommenda- tions (CEB-FIP – Guide to durable concrete) pre-empts this by suggesting an overall project advisor or advisory team, who is taken on board even from the time of planning the facility and will be associated with construction, and will also be available for formulating finally the maintenance document. The possibility of augmenting the project advisors, as and when required, should also be appreciated.

    Durability and Performance

    The aspects related to effective planning, design, construction and maintenance have to ensure that the constructed facility is having the required performance. The various reasons for deterioration and corrosion of these constructed facilities and the methods to redress should be understood explicitly. These will help not only in ensuing a appropriate rehabilitation strategy, but will also help in addressing such a possibility even from the planning, design, construction and maintenance of the facility.

    The various aspects related to the parameters influencing the repair and rehabilitation strategies for addressing the deterioration of concrete constructed facilities in the increasingly aggressive environments of the present day need to be re-examined from time to time. These parameters can be broadly classified into two major sections, environmental parameters and material parameters, with the material parameters including both that are relevant to the concrete or mortar and the steel in it. The primary parameter that influences the deterioration of both concrete is simply the porosity of these materials that allow the permeation of the aggressive environment into it over a period of time. The characteristic that influences the time to initiation of corrosion initially and later the cracking of concrete is also the porosity. The reinforcement is generally in a passive state up to initiation of corrosion and after initiation, it is influenced by the environment in concrete up to cracking and later by the environment itself. The broad relationships between these and repair strategies have also been looked at and their effectiveness is explained.

    NBMCW February 2012

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