Cracks in the concrete patio are a common maintenance issue among households with concrete driveways and sidewalks. To solve this problem, use of reinforced concrete is recommended. In this method, a steel bar is inserted into the concrete mix. This bar or the rebar, binds with the concrete through a chemical bonding process that cannot be broken by daily wear and tear or the stress such induced by passage of vehicles. As a result, concrete reinforced with steel bar raises the overall durability of the concrete surface. The reinforcing bars also prevent concrete corrosion. Corrosion occurs due to seepage of moisture and chemical vapors within the pores of the concrete. The cement mix in contact with the rebar forms an insulating layer, neutralizing any form of chemical reaction that can cause corrosion.
Understanding the Problem
However, the installation of rebar within the concrete mix is a slightly complicated process. If not done properly, the rebar begins to poke through the concrete patio within days of the concrete mix drying-up. Often, elongated sections of the rebar start jutting through the cracked, patio surface. This is a major safety hazard and requires extensive repairing of the patio. However, this problem can be easily prevented if you understand the common reasons that cause displacement of the rebar.
Reason 1 – Improper Use of Water & Plasticizers
The amount of water used in concrete-work affects the inherent strength of the prepared patio, its drying-up duration and chances of the rebar poking through the prepared surface. You should ensure that the conventional water-cement ratio is always maintained. The minimum water measurement is about 25% of the concrete. If you plan to use more water than this, ensure that it is specifically done to hydrate a concrete mix that has specific ingredients that need excessive hydration.
An over-hydrated concrete mix is difficult-to-handle and the resultant concrete flow is misguiding. Such a mix occupies more area when pouring the concrete but later contracts, often exposing the rebar. An under-hydrated concrete mix, doesn't allow proper bonding between the rebar and the cement’s ingredients. This causes gradual shifting of the loosely-installed rebar. The rebar is gradually pushed towards a side of the patio and it eventually pokes through one of the patio’s corners.
Contemporary concrete mixes are strengthened with synthetic additives called plasticizers. They lend structural strength to the concrete and increase its overall workability by making the concrete flow, uniform. However, excessive use of a plasticizer can cause concrete congestion around the rebar. This is because presence of more plasticizer causes hard-to-detect, piling-up of concrete in small pockets around the rebar. When exposed to overlying stress induced by movement of vehicles, these inbuilt lumps disrupt, weakening the concrete-rebar bond. This dislodges the rebar from its original location, pushing it towards the upper surface of the patio.
Reason 2 – Inappropriate Rebar Calculations/Measurements
Excessive or deficient use of the re-enforcing bar is a major cause of that causes the rebar to poke through concrete patios. You should know the basic about the amount of rebar that is needed to re-enforce the concrete patio. Remember that ratio between the rebar and concrete is always tilted towards the concrete — the rebar is a small fraction of the concrete-mix. Most household beams need only 1% of rebar. Commonly, rebar percentage doesn't cross the 8%-mark for any type of household construction. It is advised that you consult someone who has expertise in this field to help you calculate the appropriate rebar percentage for your patio. This includes approximating the amount of daily footing and vehicular traffic the concrete surface would be exposed to and the local, climatic conditions.
Using an under-weight rebar can cause cracking of rebar and push small segments of it towards the patio’s upper surface. You should have a basic idea about the suitable rebar size considerations. At the time of purchasing the rebar, ask the retailer about the rebar number — commonly denoted in a series like #3, #4. Enquire about the ideal size of the patio for which each of these numbered rebars are suited. Usually, each reinforcing bar has many markings on it that can be understood as a coded form of information about its intended usage and dimensions. Inform the reinforcing-bar retailer about your patio requirements and request him to match these with this crucial bit of marked information.