Reinforced Concrete. S.Sreenath 17 May 2016

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1 Reinforced Concrete S.Sreenath 17 May 2016

2 Curing of Concrete Hardening of concrete is dependent on the presence of water. During mixing normally more water for full hydration. It is always necessary to ensure that the water is either retained or replenished to enable the chemical action to continue. A significant loss of water due to evaporation may cause the hydration process to stop. This will reduce the strength development.

3 Curing Evaporation can cause early and rapid drying shrinkage, resulting in tensile stresses which are likely to cause cracking unless the concrete has achieved sufficient strength to withstand these stressed. Curing is the process of keeping freshly laid concrete moist during initial hardening of concrete. Proper curing increases concrete strength, durability and resistance to abrasion and water tightness.

4 Methods of curing Ponding or spraying Covering of concrete Steam curing

5 Curing Time To commence as soon as the initial setting commence which is 15 to 45 minutes after placing. Curing time is the minimum period during which the concrete is kept moist. Usually curing for three to four days.

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7 Repairing of Concrete Structure Cast-in-situ concrete structures are hardly built under ideal conditions. Defects may occur as the concrete is being cast or very soon afterwards. Two mostly seen defects during construction are Cracks and Honeycombing.

8 Cracks Structural cracks. Non-structural cracks.

9 Structural Cracks Due to error in design. Loading the structure in excess of the design load, due to change in use. Error or shortcomings in the method of construction. Wrong material used. Unforeseen accident.

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11 Non Structural Cracks Too rapid evaporation of moisture from the surface of the concrete while the concrete is still plastic. Thermal contraction cracking in the early life of the concrete. Drying shrinkage cracking. Rusting of reinforcement.

14 Honeycombing Due to loss of grout under compaction or congested reinforcement.

15 Honeycombing

16 Repairing Cracks Need to investigate to determine its cause. To decide on the type of repair. Due to corrosion of reinforcement need to hack away the damaged concrete and carry out a repair. Minor cracks can fill with non shrink grout. Major cracks, pressure grouting will be required.

17 Formwork Formwork for in-situ concrete may be described as a mould or box into which wet concrete can be poured and compacted so that it will flow and finally set to the inner profile of the box or mould. Formwork to be inspected during the erection of the formwork; just prior to and during concreting and during striking.

20 Formwork Materials - Timber Extensively used. Structurally useful because of its strength in relation to its density. Comparatively easy to work to a variety of sizes and shapes either by hand or machine. It is durable under appropriate condition. It gives a good finish appearance.

21 Formwork Materials - Plywood Extensively used. It is strong and light. Supplied in sheets of 1.2m wide and length of 2.4m, 2.7m and 3m.

22 Formwork Materials - Steel Not adaptable as timber. More uses.

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25 Formwork Design Dead load of the fresh concrete and reinforcing bar is approximately 2400 kg/cum. Formwork and formwork component strong enough to support the concrete and all imposed loads. Formwork must be sufficiently rigid to prevent bulging, sagging and movement.

26 Formwork Requirements Ease of assembling and dismantling. Desirable surface finish. Tightness of joint. Ease of handling.

27 Types of Formworks System Formwork Modular design. Repetitive use.

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Introductory Chapter

Introductory Chapter Asian Concrete Model Code 2014, Introductory Chapter TABLE OF CONTENTS DEFINITIONS...3 1 INTRODUCTION... 8 1.1 SCOPE... 8 1.2 DOCUMENT ORGANISATION... 8 1.3 GENERAL PRINCIPLES... 8