High Early Strength Cement – High Early Strength Cement (HE) is a General Purpose Cement designed for use in applications where there is a desire to have enhanced early age strength gain in your concrete. HE Cement is particularly suited to concrete products, post-tensioned concrete, precast and tilt-up concrete.
What is high early strength concrete?
Introduction Rapid concrete pavement repairs have become common on many busy highways throughout North America. High early strength concrete is very useful for opening up concrete pavements to traffic earlier than conventional concrete mixtures. New pavements, full-depth repairs, and other patches can be completed and the roadway or runway opened/reopened faster than with normal or conventional mixes.
- How to get high early strength High early strength concrete (2500-3500 psi compressive in 24 hours) is usually accomplished using Type III high-early strength cement (see Table 1), high cement content (600-1000 lb/cu yd), and lower water-cement ratios (0.3 to 0.45 by weight).
- Super-plasticizers are also used to make the concrete mixture more workable during placement.
Fly ash and ground granulated blast furnace slag (GGBFS) are sometimes used in the mix to partially replace some of the Type III cement, which can be very expensive. For more information on fly ash and ground granulated blast furnace slag, consult Portland Cement Association’s publication Design and Control of Concrete Mixtures, EB001.13T.
|Type of portland cement
|Blaine fineness, m2/kg
|general concrete construction
|concrete exposed to moderate sulfate action or when moderate heat of hydration required
|high concrete strength in short time span
|suitable when low heat of hydration is necessary
|used when concrete is exposed to high sulfate action
|architectural purposes – when white or colored concrete/mortar is required
Aggregate gradation uniformity will improve concrete strength, workability, and long-term durability. Intermediate size aggregates fill voids typically occupied by less dense cement paste and thereby optimize concrete density (see Figure 1). Figure 1. Diagram showing how intermediate size aggregates fill spaces between larger coarse aggregates. It is not recommended to use calcium chloride to achieve high early strength, but if it is used, do not use more than 2%. Flash set of the concrete is likely to occur with more than 2% CaCl, and oftentimes with any amount less than 2% CaCl.
In general, the workability of the concrete mixture decreases greatly with CaCl. Insulating blankets (or other insulation measures) can also be used in the first 24 hours to help strength gain by retaining the heat of hydration. Caution must be taken, though, to avoid thermal shock when the blankets are taken off.
Thermal shock may cause premature cracking of the concrete. Considerations in using high early strength mixes Some concerns remain about the long-term durability of early-opening-to-traffic concrete repairs. This factor must be taken into account when designing reconstructed concrete pavements as well as concrete pavement repairs.
- In a few cases, early deterioration due to excessive shrinkage cracking or other environmental conditions has led to unsatisfactory performance of full-depth repairs and slab replacements.
- These distresses can be minimized by careful attention to and understanding of the effects of changes in mix design.
For more information on High Early Strength Concrete, consult ACPA’s publication Fast-Track Concrete Pavements, TB004.02P. To learn more, follow. FATQ – What are the strength tests that can be performed on concrete specimens, and how do they relate to one another? Fast-Track Concrete Fundamentals Concrete Materials Fundamentals
What is the highest strength of concrete?
In the early 1970s, experts predicted that the practical limit of ready-mixed concrete would be unlikely to exceed a compressive strength greater than 11,000 pounds square inch (psi). Over the past two decades, the development of high-strength concrete has enabled builders to easily meet and surpass this estimate.
- Two buildings in Seattle, Washington, contain concrete with a compressive strength of 19,000 psi.
- The primary difference between high-strength concrete and normal-strength concrete relates to the compressive strength that refers to the maximum resistance of a concrete sample to applied pressure.
- Although there is no precise point of separation between high-strength concrete and normal-strength concrete, the American Concrete Institute defines high-strength concrete as concrete with a compressive strength greater than 6,000 psi.
Likewise, there is not a precise point of separation between high-strength concrete and ultra-high performance concrete, which has greater compressive strength than high-strength concrete and other superior properties. See ultra high-performance concrete,
Manufacture of high-strength concrete involves making optimal use of the basic ingredients that constitute normal-strength concrete. Producers of high-strength concrete know what factors affect compressive strength and know how to manipulate those factors to achieve the required strength. In addition to selecting a high-quality portland cement, producers optimize aggregates, then optimize the combination of materials by varying the proportions of cement, water, aggregates, and admixtures.
When selecting aggregates for high-strength concrete, producers consider the strength of the aggregate, the optimum size of the aggregate, the bond between the cement paste and the aggregate, and the surface characteristics of the aggregate. Any of these properties could limit the ultimate strength of high-strength concrete.
What are the most common uses for high-strength concrete?
Admixtures – Pozzolans, such as fly ash and silica fume, are the most commonly used mineral admixtures in high-strength concrete. These materials impart additional strength to the concrete by reacting with portland cement hydration products to create additional C-S-H gel, the part of the paste responsible for concrete strength.
- It would be difficult to produce high-strength concrete mixtures without using chemical admixtures.
- A common practice is to use a superplasticizer in combination with a water-reducing retarder.
- The superplasticizer gives the concrete adequate workability at low water-cement ratios, leading to concrete with greater strength.
The water-reducing retarder slows the hydration of the cement and allows workers more time to place the concrete. High-strength concrete is specified where reduced weight is important or where architectural considerations call for small support elements. By carrying loads more efficiently than normal-strength concrete, high-strength concrete also reduces the total amount of material placed and lowers the overall cost of the structure.
How to increase the strength of concrete at early age?
The strength gain at early age can be achieved by replacing a part of the fine aggregate by flyash or blast furnace slag, without increase in the water requirement of the concrete mixture.300 + 20 Sq. M per Kg PFA required enhancing the strength, impermeability and durability of concrete. Class F PFA has to be used.