Working with Concrete
Concrete in Practice
National Ready-Mix Concrete Association (NRMCA) is the governing body that works to keep customers informed on concrete topics and ensure our work meets and exceeds high quality standards. Island Ready-Mix Concrete is dedicated to it’s customers and committed to providing the best service possible. Below are answers to some of the most common questions that arise when working with concrete. These guidelines are provided by NRMCA. Complete information on these topics can be found on the NRMCA website.
CIP 5 - Plastic Shrinkage Cracking
How to Minimize Plastic Shrinkage Cracking
- Dampen the subgrade and forms when conditions for high evaporation rates exist
- Prevent excessive surface moisture evaporation by providing fog sprays and erecting windbreaks over concrete with wet burlap or polyethylene sheets between finishing operations
- Use cooler concrete in hot weather and avoid excessively high concrete temperatures in cold weather
- Cure properly as soon as finishing has been completed
CIP 11 - Curing In-Place Concrete
What is Curing?
- Curing maintains adequate moisture and temperature in concrete at early ages so it can develop proper strength and durability
- Predictable strength gain
- Improved durability
- Better serviceability and appearance
CIP 12 - Hot Weather Concreting
High temperatures, high wind velocity, and low relative humidity can affect fresh concrete in two important ways:
1. The high rate of evaporation may cause early plastic shrinkage or drying shrinkage cracking
2. The evaporation rate can remove surface water necessary for hydration
The key to successful hot weather concreting is:
- Recognizing the factors that affect concrete
- Planning to minimize hot weather effects
CIP 14 - Finishing Concrete Flatwork
Finishing make concrete attractive and serviceable. The final texture, hardness, and joint pattern depends on the concrete's end use. Finishing should be carefully planned. Skill, knowledge and experience are required to deal with a variety of concrete mixtures and field conditions.
CIP 26 - Jobsite Addition of Water
When concrete arrives at the jobsite with a slump that is lower than that allowed by design or specification and/or is of such consistency so as to adversely affect the placability of the concrete, water can be added to the concrete to bring the slump up to an acceptable or specified level.
CIP 31 - Ordering Ready Mixed Concrete
The key to placing an order for ready mixed concrete is to provide all the basic detailed information and to keep the requirements as simple as possible and relevant to the application. Some of the basic requirements to keep in mind when placing a concrete order are:
- Size of coarse aggregate - nominal maximum size required for the job
- Slump - a measure of consistency. Stiff mixtures have low slump
- Entrained air - used if concrete will be exposed to freezing temperature in service or during construction
- Quality level required - in terms of properties and composition