Rebar and Concrete Work: Checking Quality

Once concrete is poured, reinforcement can no longer be seen. What a client can check at the formwork, rebar, concrete delivery, pouring and curing stages.

Reinforced concrete structures are the skeleton of a house, and their quality cannot be hidden later by any finish. At the same time, most of this work becomes concealed within a few hours: once the concrete is poured, the number, position and connections of the bars can no longer be seen. That is why checks happen before the concrete truck arrives. A client does not need to be an engineer, but it is important to know what to look for.

Formwork: accuracy of shape

Formwork is the mould that gives concrete its shape. Its dimensions, plumb and level must match the design. There should be no gaps between formwork panels; otherwise cement paste leaks out and voids and honeycombing appear on the concrete surface.

The formwork must carry the weight of the concrete and the pressure generated during pouring. Slab formwork on weak props can deflect during the pour, and the slab will harden with a sag. Before pouring, the inside of the formwork is cleared of debris, timber offcuts and water.

The inner faces of the formwork are treated with a release agent so the concrete does not stick. Care is needed that the release agent does not get onto the reinforcement, as oil on the bars weakens their bond with the concrete.

Reinforcement: diameter, spacing and connections

Reinforcement must follow the layout in the drawings. The main points checked are:

bar diameter and grade;
spacing between bars;
the distance between top and bottom meshes;
links in columns and beams and how closely they are spaced;
lap lengths and connections between bars;
additional bars at openings, corners and junctions.

Reinforcement should be clean. Heavy scale, oil, mud or old mortar weaken the bond with the concrete. Light surface rust is generally not a problem, but flaking rust should be removed.

Concrete cover

There must be a set thickness of concrete between the reinforcement and the concrete surface. This cover protects the steel from corrosion and fire. To achieve it, the bars do not rest directly on the formwork but sit on purpose-made plastic or concrete spacers.

Missing spacers are one of the most common mistakes. If the bottom mesh of a slab lies on the formwork, the steel ends up too close to the surface once the concrete is poured. Years later, rust stains and spalling concrete appear at those spots.

Accepting and placing the concrete

When concrete arrives on site, its delivery note is checked: the strength class, time of dispatch and volume must match the design and the order. The workability of the mix should suit the type of element. Adding water to concrete on site makes it easier to place but reduces its strength, and this must not be allowed.

Taking sample cubes for laboratory testing is a reliable way to document quality. The cubes are tested after set periods and show whether the concrete has reached its design strength.

Concrete is placed in layers and compacted by vibration. Vibration drives out trapped air and ensures the mix fully surrounds the reinforcement. Over-vibration, however, can cause segregation, and so can dropping concrete from a height.

Curing and striking formwork

Care of the concrete starts after pouring. In hot, windy weather the surface dries quickly and can crack, so it is kept damp and covered. Cold weather brings the opposite problem: the concrete must be protected from freezing.

When formwork can be removed depends on the type of element and the temperature. Side forms for walls and columns come off sooner, while soffit forms and props under slabs and beams are removed only after the concrete has gained sufficient strength. This decision is made by the designer or the technical supervisor.

Once the formwork is struck, the surface is inspected carefully. Honeycombing, exposed reinforcement, cracks and dimensional deviations are recorded. Minor surface defects are repaired with purpose-made repair mortars, while structurally significant defects are dealt with on the structural engineer's instructions.

Documentation

Before each pour, the reinforcement is accepted with a concealed-work record and photographed. Concrete delivery notes, sample test results and pour dates are kept. This archive remains valuable after construction: if an extra storey or alterations are planned in future, the structural engineer will rely on it.

Zaferoğlu İnşaat has a team of professional tradespeople experienced in working with modern construction technologies. You are welcome to discuss the organisation of reinforced concrete work on your project with us.

News