High-early-strength concrete can be developed using ordinary concrete constituents, special admixtures, and certain concreting practices. The high-early-strength concrete, which is also called fast track concrete, gains its specified strength at an early age compared to ordinary concrete.
The time during which the concrete should achieve the specified strength ranges from a few hours to several days. The high-early-strength concrete is used for rapid form reuse, precast concrete for fast production of elements, high-speed cast-in-place construction, cold-weather construction, quick repair of pavements to reduce traffic downtime, and fast-track paving.
How to Develop High-Early-Strength Concrete?
The high early strength can be achieved using one or a combination of the following strategies. The selection of the high early strength production strategy based on the time during which the concrete should get designated strength:
1. Type III Portland Cement
Type III or high-early-strength cement is a type of Portland cement that reacts quickly than conventional cement or Type I cement. The high-early-strength cement achieves around seventy percent of its 28-day strength in three days. The initial set of concrete made with Type III cement is within 45 minutes, and the final set is around 6 hours.
2. High Cement Content
The increase in cement content (400 to 600 kg/m3) is another way of producing high early strength concrete.
3. Low Water-cementing Materials Ratio
The reduction of water to cementing material ratio ranging from 0.20 to 0.45 by mass can produce high-early-strength concrete. Water to cement material ratio of 0.32 to 0.42 has been used to produce high-early-strength concrete, whereas the use of w/cm of 0.20 can produce very-high-early-strength concrete.
4. Higher Freshly Mixed Concrete Temperature
Hydration of cement increase as the temperature of freshly mixed concrete increases. So, the increase of newly mixed concrete temperature would increase the process of strength development in concrete, and hence high early strength concrete is obtained.
5. Chemical Admixtures
Accelerating admixtures are available to produce high-early-strength concrete. Calcium chloride, which is standardized by (ASTM D 98), is an example of an accelerating admixture that is used to produce high early strength concrete. The accelerating admixture increases the rate of hydration of concrete and early strength development of concrete.
6. Supplementary Cementitious Materials
The use of supplementary cementitious material in concrete can produce high-early-strength concrete. The combination of ground granulated blast furnace slag and higher curing temperature leads to the increase of high early strength development of concrete.
7. Steam or Autoclave Curing
The steam or autoclave curing is an effective way of high-early-strength concrete production. The concrete compressive strength achieved under autoclave in 24 hours is equivalent to concrete compressive strength that can be achieved in 28 days under normal curing conditions.
The concrete under autoclave curing has better sulfate resistance, and lower drying shrinkage compared with concrete under normal curing conditions, in addition to the elimination of effloresce.
8. Insulation to Retain Heat of Hydration
The use of insulation to trap heat in fresh concrete is another technique to produce high-early-strength concrete.
Read More:
5 Monitoring Techniques for Early Strength Gain of Concrete in the Field
FAQs
The high early strength concrete is achieved through the use of one or combination of type III Portland cement, high cement content, low water to cementitious materials, high freshly mixed concrete, chemical admixtures, supplementary cementitious materials, autoclave curing, and insulation of concrete to retain its heat of hydration.
Type III or high-early-strength cement is a type of Portland cement that its reactions quicker than Type I cement. The high early strength cement achieves around seventy percent of its 28-day strength in three days.
It is advantageous when early stripping of forms is needed, or a structure needs to be put into service quickly.
The steam of autoclave curing is an effective way of high early strength concrete production. The concrete compressive strength achieved under autoclave during in 24 hours is equivalent to concrete compressive strength that can be achieved in 28 days under normal curing conditions.
Accelerating chemical admixture increases the rate of hydration of concrete and early strength development of concrete.
The high early strength concrete used for rapid form reuse, precast concrete for fast production of elements, high-speed cast-in-place construction, cold-weather construction, quick repair of pavements to reduce traffic downtime, and fast-track paving.