Concrete is one of the most prevalent building materials known to man. From roadways to houses and just about everything in between, you’ll find concrete in it somewhere. Many people believe that cement and concrete are the same thing. They aren’t. Each has properties that make it distinct from the other, and these properties are what make them useful in different applications. When concrete is poured, being basically a liquid, it needs something to keep it in the shape that you want or need. You’ll read about what these are and how they are used and cared for. The process by which concrete solidifies is known as curing. How curing occurs and what occurs during the curing process will be discussed. Advanced concrete building concepts such as pre-cast homes and expansion joints will be discussed in detail. How do you know how much concrete a specific job will require? You’ll find out how to make this determination. Concrete by itself is pretty strong, but there are ways to make it even stronger, and these will be discussed below. The use of concrete in areas that experience seismic activity is very prevalent, but there are certain precautions that must be taken in this type of area that aren’t required in other areas. Concrete is affected by weather and environmental conditions. Concrete preservation is important and you’ll read about some methods for concrete preservation. This Engineering Guide to Concrete will present you with some best practices to make your use of concrete more efficient and productive by giving you a more thorough understanding of concrete.
The Various Types of Concrete and Cement
Before discussing the various types of cement, an introduction to concrete and how it is made will give you a firm groundwork to begin your study. Portland cement composition and manufacturing will be discussed. Once we have this groundwork established, we will begin by looking at self-compacting concrete. Engineered cementitious composite (CEC) is a type of concrete compound that is flexible, a unique property that makes it useful for a variety of uses. This concrete product and its uses will be discussed below.
The Use of Forms in Concrete Construction
Concrete is considered a liquid. As a liquid, it tries to find its lowest point. This means that without a way to keep concrete where you want and in the shape that you want it in, it’s a pretty useless building material. Keeping control of concrete is accomplished by the use of forms. These can be wood, metal, or a variety of other materials. The basics of concrete formwork will be discussed. Next you’ll read about how people in the concrete construction industry use and reuse forms. Once you know the basics of what forms are and how they’re used and cared for, the next logical step is to learn about the newest types of forms that are being used in the field. To top off this discussion, you’ll learn how cement walls are designed.
All about the Concrete Curing Process
The process by which concrete dries and thus hardens is called curing. The curing of concrete and cement is an exothermic one. This means that heat is given off as the concrete hardens. In this section you will become familiar with this curing process. You will also be presented with a number of tips to help your poured concrete cure properly. Cold, wet environments present some challenges to the curing process. But there are ways to get around these challenges; you will be presented with ways to get around these challenges and cure your concrete.
Advanced Concepts of Concrete Building
Many houses and buildings are built with slab foundations- foundations which aren’t just around the perimeter of the house, but are under the whole house. For most houses and buildings, a single slab will suffice. However, much larger houses and buildings, even in non-seismically active areas, need to be able to move and settle. This is accomplished with expansion joints. The theory and practice of expansion joints will be thoroughly discussed below. One way to obtain greater strength and insulation when building residential buildings is by the precast method. This method will be discussed in this section as well.
Calculations When Using Concrete
You want to build a patio, but you need to figure out how much concrete you will need for it. How do you figure that out, in such a way that you don’t either have to keep going back to the home improvement store for more bags of concrete or call the cement supplier and ask for another truck? There are calculations, which will be discussed below, that will tell you how many cubic yards you need and how many bags that translates into. You will also be given methods for determining the amount of cement present given a given quantity of concrete.
Making Concrete Stronger
By itself, concrete is pretty strong. But when it’s used as a building material, it doesn’t have enough strength to have the required amount of longevity. Add in outside stresses such as wind and rain, and it begins to look almost weak. There are many different ways in which concrete can be engineered that greatly enhance the underlying strength of the concrete. Some of these engineering methods that can be put into practice include glass fiber and steel reinforcing, to name a few. The various methods by which concrete can be strengthened are discussed in detail below.
New Earthquake and Structural Concrete Specifics
Seismic activity is the single greatest factor in decreasing the longevity of concrete structures. Using pre-stressed concrete or one of the other methods of reinforcing the concrete structure is one way to ensure that a concrete structure will remain standing during an earthquake. There are a number of methods that concrete engineers have at their disposal to make concrete structures earthquake resistant. Some of these methods will be discussed below.
Preserving and Repairing Concrete
Whether you’re responsible for maintenance on a bridge, a house, or any other type of structure that contains concrete, preservation of the structural integrity of that structure’s concrete should be of prime importance to you. Many environmental factors affect the longevity of the concrete portions of the structure. Cracks are the main enemy of concrete and you’ll be given information on what causes cracks and how to repair cracks in foundations and other areas of your building.
Concrete Curing Underwater, in Freezing and Hot Temperatures, and in Humid Conditions
Curing means hardening of concrete mix under controlled conditions. Temperature and moisture content of concrete are two important aspects of curing and depending upon these two factors, concrete achieve its strength. Efficient curing ensures that concrete is durable, resistive to corrosion and is resistant to wind and heat. Period of curing is different for different types of work and temperature conditions. In wet and freezing conditions conventional methods do not work.
Underwater or Underground Curing of Concrete
Underground construction always poses serious threats to curing of concrete. For example, underground curing of concrete in tunnels is always affected by seeping water. The surface always remains wet and setting of concrete takes time, rendering it weak and unstable. Similarly working on a basement or foundation also has moisture issues. Working in watery conditions requires waterproofing, which increases costs and secondly drying the area also takes plenty of time. As far as underwater tunnel construction is concerned, the immersed tube tunnel method is an effective way to reduce costs and construct a stable tunnel that is least affected by water or moisture seepage.
Similarly, curing of concrete in wet conditions needs special care and treatment; you cannot just place it and forget about it. Despite the fact that curing is not possible without water, too much water will definitely render the concrete weak and result in cracks on the surface. In regions with high rainfall, concrete curing in time becomes very crucial. Similarly in wet and waterlogged conditions, curing needs to be done carefully. If the surface is too wet, the first thing to do is to dry the surface by heating. It may not be possible to dry the surface completely and that is where the free water to cement ratio becomes crucial. This ratio must be set according to the moisture content of the surface because if the water cement ratio exceeds the desired limits, it will result in capillary pores on the set concrete, resulting in poor strength and durability. Additives can also be used to speed up the process of concrete setting.
Concrete Curing in Freezing Conditions
Construction in freezing areas is a difficult task; snow does not allow you and your concrete to settle down. Hydration of concrete, or rather the setting of concrete, is greatly affected if the temperature is below zero degrees Celsius. The first thing before to do before placing the concrete is to clean the surface. Putting concrete on an icy surface is a waste of money and resources straightaway. Use hand picking tools and scratching tools so that the surface allows a certain amount of friction for the concrete to hold onto the surface. Secondly, after the concrete is placed, using heat preserving techniques will help. Increasing the heat of hydration of concrete results in better curing and setting. Insulating sheets, straw-plastic, insulating blankets, and windbreaks can be used because they help in increasing or at least maintaining a constant heat of hydration. However, if the temperature is below 20 Degree F, simply skip the idea of placing concrete because it will lead you nowhere as hydration stops completely at such temperatures.
Here is in-depth description of things to do for curing concrete in below freezing temperatures.
- Stick to the design code, maintain proper water-cement ratio, and ensure a safe gap between the reinforcement bars. The water to cement ratio should not be more than 0.40 in wet and freezing conditions.
- In extremely cold regions, a propane heater and a polyethylene enclosure can be used to keep the temperature above the freezing point.
- Wet and freezing conditions mean moisture, which means corrosion when related to steel and concrete. Use Portland Type III cement as it helps in easy setting without degrading the quality of concrete.
- Use additives like fly ash, silica fume, and furnace slag as they help in controlling formation of chloride ions, which is one of the main reasons for steel corrosion in concrete.
- Concrete under water curing for flatwork applications becomes easy with previous concrete. Previous Concrete is all coarse aggregates and it contains a negligible percentage of fine aggregates, especially sand. Additives are mixed into it that do not allow water to penetrate inside the concrete surface. Previous concrete is suitable for constructing pavement as it does not soak in water but allows gallons of water pass through it without damaging concrete pavement and strength.
- Use concrete sealants so that water does not seep inside the concrete. Sealants not only increase the life of concrete but also help in preventing concrete curing failure. In extremely cold regions, only a breathable concrete sealant must be used, as it will allow the evaporation of water and moisture, helping in fast setting of the concrete.
Concrete Curing in Hot Conditions
Even in hot conditions, curing requires special attention. The problems in such conditions are opposite of those in cold conditions. In very hot and humid regions, heat loss and continuous evaporation results in lack of moisture from the surface of concrete and thus leads to cracking. Such weather conditions require a high water-cement ratio, which means the strength of concrete is going to be affected. In such conditions retarding agents can be used. Using Type II cement is also helpful as it generates less heat and helps in preserving moisture content. An adequate supply of water, and keeping the concrete wet after placement, is important so that concrete does not crack and strength is not compromised at all.