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What is the function of primers in joint sealant?

Most joint sealants applied in concrete joints are adhesive and the recommended joint width/depth of joint sealant is from 2:1 to 1:1 as given by BS6213 and Guide to Selection of Constructional Sealants. When joint sealant is applied on top of joint filler in concrete joints, additional primers are sometimes necessary because:

(i) Primers help to seal the surface to prevent chemical reaction with water;

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What is the purpose of using movement accommodation factor for joint sealant?

Movement accommodation factor is commonly specified by manufacturers of joint sealants for designers to design the dimension of joints. It is defined as the total movement that a joint sealant can tolerate and is usually expressed as a percentage of the minimum design joint width. Failure to comply with this requirement results in overstressing the joint sealants.

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What are the functions of different components of a typical expansion joint?

In a typical expansion joint, it normally contains the following components:

joint sealant, joint filler, dowel bar, PVC dowel sleeve, bond breaker tape and cradle bent.

Joint sealant: It seals the joint width and prevents water and dirt from entering the joint and causing dowel bar corrosion and unexpected joint stress resulting from restrained movement.
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Can a concrete structure be completely free of expansion joints and contraction joints?

Consider that the concrete structure is not subject to the problem of differential settlement.

For contraction joints, it may be possible to design a concrete structure without any contraction joints. By using sufficient steel reinforcement to spread evenly the crack width over the span length of the structure, it may achieve the requirement of minimum crack width and cause no adverse impact to the aesthetics of the structure. However, it follows that the amount of reinforcement required is higher than that when with sufficient contraction joints.

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If on-site slump test fails, should engineers allow the contractor to continue the concreting works?

This is a very classical question raised by many graduate engineers. In fact, there are two schools of thought regarding this issue.

The first school of thought is rather straightforward: the contractor fails to comply with contractual requirements and therefore as per G. C. C. Clause 54 (2)(c) the engineer could order suspension of the Works. Under the conditions of G. C. C. Clause 54(2)(a) – (d), the contractor is not entitled to any claims of cost which is the main concern for most engineers. This is the contractual power given to the Engineer in case of any failure in tests required by the contract, even though some engineers argue that slump tests are not as important as other tests like compression test.

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