10 Easy Steps To Pouring Your Own Concrete Project
Step One – Plan Ahead
Laying out your project is an important first step! Stake out your project area. Remove grass, tree roots, etc. Check the grade to ensure proper drainage. Also, be sure to use graph paper and sketch out your project by using the one square equals one foot approach.
Step Two – Forming the Area
The most common forming materials are either 2 x 4’s or 2′ x 6’s. These are placed on the edge to surround the area to be poured. In general, concrete should not be poured at a thickness of less than the width of a 2 x 4. Use stakes on the outside of the form to hold it in place. Note: The stakes must not extend above the form or they will interfere with the “screeding” procedure. Check the grade of the area by moving the “screed” board across the forms and measuring the distance from the board to the grade of the area.
10 Steps to Durable Exterior Flatwork
1. Use the right concrete
The Ontario Building Code requires that all exterior concrete shall have a minimum 28-day compressive strength of 32 MPa and a maximum water/cementing materials ratio (W/CM) of 0.45 (C-2 Concrete as per CSA A23.1) and 5-8% air for freeze-thaw durability. 25 MPa concrete should never be used! Concrete should only be ordered from an RMCAO member company.
2. Use the right contractor
Use a contractor who has been trained to an industry certification program such as ACI Concrete Flatwork Finisher/Technician (or similar). Ask for past examples of their work and references. Call the references and visit projects that have gone through at least two winters.
Concrete Driveways
The average homeowner will not normally be able to install a concrete driveway without expert assistance. It is strongly recommended that a qualified contractor be engaged to ensure a satisfactory job.
To provide a quality driveway, the following guidelines should be carefully observed.
(Concrete should be placed between April and September. If placed outside this time frame, additional precautions will be necessary.)
1. Determine The Required Thickness (Minimum)
- For cars and pick-ups 100 mm
- For light trucks 125 mm
- For occasional heavier trucks 150 mm (placed on competent subgrade)
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2. Site Preparation
Concrete can be placed directly on uniform subgrade after removing the topsoil, or on deteriorated asphalt pavement. Excavate or bring to grade as necessary using granular ‘A’ as leveling course (typically 100 mm).
Residential Concrete Requirements
Proper Concrete Jointing Details to Control Random Cracking
The primary factors that result in concrete shrinkage and/or cracking include:
- Settlement of the sub-grade
- Chemical shrinkage of the concrete
- Temperature and moisture changes in the concrete
- Application of loads to the concrete surface
- Restraint of concrete movement during either expansion or contraction.
The actual amount of concrete shrinkage is governed by:
- The concrete’s raw constituents
- The unit water content of the mix
- The drying conditions that the concrete is exposed to
- The size and shape of the concrete element.
Sealers for Concrete Flatwork
In general, there are two types of sealers available for use:
- Film Forming Sealers – Sealers that bond to the top surface of the concrete provide a barrier to the ingress of liquids.
- Penetrating Sealers – Sealers that are absorbed into the concrete surface and block the pore structure of the concrete preventing further water penetration.
Selection of the proper concrete sealer is based upon understanding the required concrete surface finish and the exposure conditions and traffic type (vehicles, pedestrian, etc.) that the sealer will be exposed to. It is strongly recommended that you discuss your application with the sealer manufacture prior to the start of the project. The factors that should be considered include:
What Every Homeowner Should Know About Concrete
What is concrete?
In its simplest form, concrete is a mixture of paste (cement & water) and aggregates (sand & stone). The paste coats the surface of the fine (sand) and coarse (stone) aggregates and binds them together into a rocklike mass known as concrete. In addition to paste and aggregates, concrete may also contain highly specialized chemical admixtures that enhance the specific properties of concrete. Chemical admixtures are used to improve both the workability and/or the durability of concrete.
Within this process lies the key to a remarkable trait of concrete: it is plastic and can be molded or formed into any shape when newly mixed, and is strong and durable when hardened. These qualities explain why concrete is a primary building material throughout the world that is used to construct everything from skyscrapers, bridges, highways and dams to sidewalks, curbs, patios and houses.
Hot Weather Concrete
Hot weather concreting conditions typically include:
- High ambient air temperatures (? 28°C)
- Low relative humidity conditions
- High wind speeds
- Solar radiation or heat gain
These conditions can result in the following challenges for the concrete contractor:
- Increased concrete water demand
- Accelerated concrete slump loss
- Increased rate of setting leading to placing and finishing difficulties
- Increased tendency for plastic shrinkage cracking
- Increased concrete temperature resulting in lower ultimate strength
- Increased potential for thermal cracking
Cold Weather Concreting
- When the air temperature is ? 5°C.
- Or when there is a probability that the temperature may fall below 5°C within 24 hours of placing the concrete.
Because the hydration process is a chemical reaction it is strongly affected by ambient air and subgrade/formwork temperatures. At low temperatures concrete gains strength and sets very slowly and must be adequately protected from freezing and thawing. Concrete that is allowed to freeze while in its plastic state can have its potential strength reduced by more than 50% and its durability properties will be dramatically reduced. Concrete must achieve at least 3.5 MPa before it is frozen and should obtain at least 20 MPa before it is exposed to multiple freeze/thaw cycles.
