CONSTRUCTION JOINTS IN-SITE CONCRETE METHOD STATEMENT

Introduction:

In this article, you will know how to create strong construction joints according to contract rules. From planning to concrete placement and sealing, it covers each step clearly for successful project outcomes.

1. Scope

This procedure outlines the methods to be used for constructing effective and durable construction joints according to the contract specifications.

2. Procedure

2.1 Planning

Some cases, the client must prepare shop drawings proposing the location and type of construction joints and obtain approval from the consultant’s representative before proceeding with the work.

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2.2 Horizontal Surfaces

Laitance Removal: To ensure a good bond when fresh concrete is placed, laitance (a thin layer of cement and fine particles on the surface) must be removed from the concrete. This can be done using various methods:

Washing and Brushing: Brush off laitance while the concrete is still fresh but slightly stiffened, typically within one to two hours after placement. Use soft and hard-bristle brushes depending on the concrete’s stiffness.

Air and Water Jet: Direct a jet of air and water onto laitance within six hours of placement, or longer if deemed appropriate. Avoid starting too soon to prevent dislodging coarse aggregates.

Mechanical Scabbling: If laitance is too hard for brushing, use small percussion power tools after 3 days when the concrete has hardened enough. Be cautious not to weaken coarse aggregates.

Abrasive Blasting: Wet or dry abrasive blasting can be used to expose aggregates. Take special safety precautions when using sand.

2.3 Timing

Deciding the right time to treat the joints depends on the concrete’s setting and hardening rate, which is influenced by temperature.

2.4 Preparing for the Next Pour

If there’s even a short delay before the next concrete pour, protect protruding reinforcement. Remove rust, loose mortar, or other contaminants from bars before the next pour.

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2.5 Vertical Surfaces

Stop Ends/Expanded Metal Mesh: Vertical joints are usually formed at the top end of the formwork. Care must be taken to avoid grout loss in holes for reinforcement in stop-ends. In some cases, proprietary stop-ends encase bent bars in expanded plastic foam to prevent grout loss. Avoid using impact to straighten bent steel at stop-ends, as it can cause brittle fractures.

Formwork: Ensure formwork for subsequent concrete pours is accurately aligned and securely fixed to prevent grout leaks, discoloration, and honeycombing. Foam rubber or polyurethane strips can be used around the joint’s edge.

2.6 Vertical Joint Surface Preparation

The same methods for horizontal surfaces (washing and brushing, mechanical scabbling, and abrasive blasting) can be used for vertical joints. Exercise caution to avoid damaging leading edges.

2.7 Watertight Construction

In watertight construction, flexible water bars may be used as specified. Ensure water bars are securely tied during concreting to prevent folding.

2.8 Cold Joints

Detection: Cold joints occur when adjacent concrete placement is delayed, and the earlier concrete has stiffened. Embed a poker vibrator into the existing concrete to check its condition. If a distinct hole forms, do not continue concreting. Prepare the joint face for horizontal construction joints.

2.9 Placing Fresh Concrete

When placing new concrete on or against old concrete:

o Remove any dirt or dust from the old concrete surface with a compressed air hose, wearing safety goggles.

o Clean the surface before fixing the new formwork to prevent dirt from sticking to the new formwork.

2.10 Joint Sealing

For structural components exposed to the external environment, joints must be sealed to prevent water ingress. Refer to the contract specifications and/or manufacturer’s instructions for the type and method of application.

3. Documentation

Maintain the following documentation as required by the Project Quality Plan and contract specifications:

o Contract and/or approved workshop drawings.

o Manufacturer’s test certificates (for sealants and water bars).

o Request for Consultant’s consent/approval.

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