CONCRETE CHARACTERISTICS BASIC AND CIVIL ENGINEERING TUTORIALS

CONCRETE CHARACTERISTICS BASIC INFORMATION
What Are The Characteristics Of Concrete?


Characteristics of Concrete
1) Convenient for use: the new mixtures have good plasticity that can be cast into components and structures in various shapes and sizes.

2) Cheap: raw materials are abundant and available. More than 80% of them are sand and stone whose resources are rich, energy consumption is low, according with the economic principle.

3) High-strength and durable: the strength of ordinary concrete is 20 - 55MPa with good durability.

4) Easy to be adjusted: the concrete with different functions can be made just by changing the varieties and quantities of composing materials to meet various demands of projects; steel bar can be added to concrete to improve its strength, and this kind of concrete is a composite material (reinforced concrete) which can improve its low tensile and bending strength in order to meet the needs of various structural engineering.

5 ) Environment-friendly: concrete can make full use of industrial wastes, such as slag, fly ash and others to reduce environmental pollution. Its major shortcomings are high dead weight, low tensile strength, brittle and easy to crack.

CEMENT PASTE CORROSION PREVENTION BASIC AND TUTORIALS

CEMENT PASTE CORROSION PREVENTION BASIC INFORMATION
How To Prevent Corrosion Of Cement Paste?


The corrosion of cement paste occurs because chemical reaction can happen between its external environment and internal environment. The corrosive compound must be the solution with a certain concentration, such as high temperature, proper humidity, fast flow, and the corrosion of steel bar.

Thus, the following measures can be adopted in the use of cement:

1) Select the cement varieties reasonably based on the features of the erosive environment. For example, the cement whose hydrates contains a little calcium hydroxide has high capacity to resist erosive effects of soft water and others; the anti-sulfate cement whose content of tri-calcium aluminate is less than 5% can resist the sulfate erosion.

2) Raise the Density of Cement Paste. The amount of mixing water for Portland cement should be strictly controlled in order to reduce the pore space.

The water theoretically needed in hydration of Portland cement is only 23% but much more mixing water (accounting for about 40%-70% of the cement mass) is needed in practical projects, and the pores connect to each other after the excessive water evaporates, so the erosive media go through the inner part of cement easily to accelerate the corrosion of cement.

The mix proportion should be designed reasonably in order to improve the compactness of cement concrete. Low water-cement ratio and the best construction method should be adopted as much as possible.

In addition, the insoluble calcium carbonate shell or calcium fluoride and thin silica gel film generated by conducting carbonization or fluosilicic acid treatment on the surface of concrete and mortar can increase the compactness of the surface and decrease the infiltration of erosive media.

3) Add a Protective Layer. The resistant stone, ceramic, plastic, and waterproof material are covered on the surface of cement paste, forming a impermeable layer for protection, to prevent the corrosion media contacting with cement paste directly.