Concrete is as old as construction itself, and cement is one of the most important ingredients used for producing concrete. There is virtually no other building material that has so greatly contributed to the development of human civilization. Cement went through many changes and improvements in the nineteenth and twentieth centuries.
Cement is defined as a powder of alumina, silica, lime, iron oxide, and magnesium oxide burned together in a kiln and finely pulverized and used as an ingredient of mortar and concrete.
Concrete is a composition of materials (coarse and fine aggregates) that when mixed with a binding material cement and water reacts chemically to form a solidified composited rigid material.
Concrete is the most popular construction material in the world due to its durability, safety, economic relevance, and sustainability.
It is frequently used for:-
• Foundation and Driveways
• Columns, Caissons, and Piers
• CMU (Concrete Masonry Units)
• Walls and Beams
• Bridges and roads
• Precast and Pre-stressed Elements
Materials Used to Make Concrete for General Use:-
• Hydraulic Cement (42.5R)
• Hydraulic Cement (ASTM C 1157) includes a mixture of a pozzolanic material which is volcanic ash this is used as a cement extender that improves the strength and durability of the cement. It also reduces the costs of producing concrete.
• Coarse Aggregates Crushed, Natural or manufactured (ASTM C 33)
• Fine Aggregates Crushed, Natural or manufactured (ASTM C 33)
• Potable/drinking water
• Air/ Induced by mixing
Hydraulic Rock Hard Cement – Accelerated Early Strength
In the construction industry, “Accelerated Early Strength” is regarded as a concrete that achieves a loading strength in a matter of hours.
Rock Hard Cement supplies two types of hydraulic cement:- 42.5R (rapid) and 52.5N (normal) strength class cement for concrete production. Both types of cement can produce high strength concretes of +50-70MPa. The 42.5R cement can produce the same high strength concrete as the 52.5N strength class cement, due to it having similar 2day and 28day strength requirement as the 52.5N cement. The difference between the two is that 42.5R is rapid drying and best for small home projects while the 52.5N allows for transportation of ready-mixed concrete from central mixing stations to job sites, time for workability/application and then the accelerated early strength on drying.
Time is crucial on many concrete projects however contractors also require maintaining quality and durability while reducing construction time to reflect a greater bottom line. That is why many concrete producers and contractors are turning to Rock Hard Cement to meet tight schedules. Rock Hard Cement is one of the most durable types of cement on the market. Its rapid-setting properties cause it to be an ideal solution for today’s schedule and budget-driven projects.
The correct mixing and proportioning of materials are essential to ensure that concrete achieves the desired strength, durability and consistency as well as maintains it’s affordability.
• It is critical when mixing concrete to have the correct proportioning of coarse and fine aggregates as to prevent segregation, bleeding and poor finish.
• Water-cement ratio must be controlled; the addition of water often weakens the concrete mixture causing lower compressive strength as well as several physical defects; dusting, aggressive plastic shrinkage cracks etc.
• Using the correct quantity of cement is also critical in ensuring that the concrete remains cohesive and can maintain its compressive strength.
• Concrete mix proportioning is done by the volume method.
1 The volume of cement equivalent to two 18 litre buckets
2.5 Volume of fine aggregate equivalent to five 18 litre buckets
3.5 Volume of coarse aggregate equivalent to seven
21 Litres of water
Slump 150mm (6’’)
The amount of mixing water in concrete is a major factor in its durability. In a typical concrete mix using hydraulic cement, nearly all the water used in the mix is used up in the hydration process resulting in a dense concrete with very low drying shrinkage.
Voids or pores in concrete, along with drying shrinkage cracks, provide routes of entry for substances that attack the concrete and its reinforcement. With fewer pores and less drying shrinkage, rapid-hardening hydraulic concrete seals the concrete and mitigates these defects.
The use of vibrators is extremely important to ensure that the concrete is free from voids. It also helps to consolidated concrete and mitigates against cracking, leaks and trapped air. These physical defects can cause a reduction in the service life of the concrete. Entrapped air can be as high as 20 % without proper vibration
The correct balance between proportions is crucial to the desired consistency and can be achieved by doing trial mixes. This will ensure that a correct mixing proportion is achieved based on the type of aggregates used i.e. Crushed limestone (Type M Sand) VS Natural occurring Brown Sand.
Different types of materials have different properties and can cause different effects in the mixing proportions:-
When water is added to cement, it triggers a chemical reaction called hydration. When an excessive amount of water is added then it increases the water-cement ratio and ultimately there is a decrease in its strength when it hardens. Similarly, when less amount of water is added the cement isn’t properly hydrated therefore the required concrete strength is not achieved.
The below testing is recommended on trial mixes prior to application to achieve the desired consistency.
The finishing of concrete is also very important in assisting the concrete to reduce cracking and protect the concrete surface from the elements (environment).
Mixing, transporting, and handling of concrete should be carefully coordinated with placing and finishing operations. Concrete should not be deposited more rapidly than it can be spread, struck off, consolidated, bull-floated and deposited continuously as near as possible to its final position.
Vibration is the most widely used method for consolidating concrete. When concrete is vibrated, the internal friction between the aggregate particles is temporarily destroyed and the concrete behaves like a liquid; it settles in the forms under the action of gravity and the large entrapped air voids rise more easily to the surface.
TIME: For a contractor or owner, time is of the essence. On many jobs, bonuses offered for getting a job done on time or a project completed earlier is money well spent. Today’s schedule-driven projects require quick construction solutions and cost savings wherever possible. Using less material and less labour saves a great deal of money.
The most used onsite proportionate mixing ratio is:
(1 cement + 2.0 fine aggregate + 3.0 Coarse aggregate + 1.30 water) =W/C 0.55
With Hydraulic Rock Hard Cement 42.5 R, the ratio for 3750 psi cube is as follows:
(1 cement + 2.5 fine aggregates + 3.5 Coarse aggregate + 1.30 water) = W/C 0.55
On average 14.5% more volume that can be used and still maintain structure and strength.
With Hydraulic Rock Hard Cement 42.5R, the ratio for 3000 psi cube is as follows:
(1 cement + 3.0 fine aggregates + 4.0 Coarse aggregate + 1.40 water) = W/C 0.60
On average 25% more volume that can be used and still maintain structure and strength.
ROI: Concrete is inexpensive, even for bigger jobs, and especially when compared to other building materials. Because it’s so universally appealing, functional, and long-lasting, it tends to yield a tremendous ROI. Upgrading your walkways, driveways, or other outdoor areas with concrete can significantly increase the value of your home for the long term.
Rock Hard Cement has a much smaller carbon footprint than other cement. During the production process, it reduces CO2 emissions by 32% to 36% over conventional cement manufacturing procedures. This is because hydraulic cement is produced at lower temperatures, so less fossil fuel is required. It also requires less limestone per ton, further reducing CO2 emissions.
Concrete buildings help to meet sustainability goals by reducing the urban heat island effect and easily support “green roof” projects.
The Leadership in Energy and Environmental Design (LEED) Green Building Rating System TM provides standards for what constitutes a “green building.” It aims to rate the energy and environmental performance of a building and encourages market evolution toward sustainable design and construction. Concrete can contribute over 20 points toward the minimum 26 points needed to qualify for a LEED TM Canada certification as noted on http://www.concretesask.org/resources/why-is-concrete-better
Concrete is versatile, long-lasting and durable as well as a cost-effective, sustainable choice for both residential and commercial buildings. When built with concrete, it’s guaranteed to last.
Concrete is a durable building material that gains strength over time and conserves resources by reducing the need for reconstruction. It resists weathering, erosion and natural disasters, needs few repairs and little maintenance, adding up to a solid investment.
Contractors across the Caribbean have realized the benefits of using Accelerated Early Strength Rock Hard Cement on a diverse range of projects. Compute the cost of durability and time, and it is apparent that Rock Hard Cement is a viable, cost-effective cement.
Rock Hard Cement is the choice for cost-effective, climate resilient homes across the Caribbean.
Rock Hard Cement Barbados recently hosted a seminar to educate its customers on the technical knowledge and benefits when working with Rock Hard Cement. The presentation was conducted by Jerome Chrysostom – Caribbean Concrete Expert.