Today, making small home accessories from concrete has become quite common. With cement and some aggregate, you can create concrete objects such as candle holders, candlesticks, flowerpots, bowls, vases, and many other decorative products for your home. Once crafted, these concrete objects can be painted and colored to suit your taste, adding a personalized touch to your decor.
How to Make Concrete Objects with Calcium Aluminate Cement, What are the Phases?
Calcium aluminate cements are used for special applications where their unique properties can be benefitted when mixed with suitable aggregates. Advantages of working with calcium aluminate cement concretes can be listed as cold weather workability, resistance to high temperatures, resistance to mild acids and alkalis, resistance to sulphates, sea water and pure water. Calcium aluminate cement concretes develop the strength that Portland cement concrete can achieve in 28 days, in 24 hours.
Another significant issue in concrete production is the selection of appropriate aggregate. Concrete aggregates consist of geological materials such as gravel, sand, and crushed rock. The size of the particles determines whether it is coarse aggregate (e.g., gravel) or fine aggregate (e.g., sand). Aggregates help making concrete mixtures more compact. They also reduce cement and water consumption and contribute to the mechanical strength of concrete.
We should pay attention to the following parameters in order to choose the appropriate aggregate.
- Gravel or crushed stone aggregates with a rough and non-glassy texture are the best ones as they form a good bond with the cement paste.
- Aggregates should be hard, chemically inert, and non-porous.
- Coarse aggregates should not absorb more than 10% of their weight once immersed in water for 24 hours.
- If aggregates absorb water of more than 10% of their weight, they are considered porous aggregates undesirable for concrete production.
- Angular and cubic coarse aggregate particles are preferred.
- The aggregate should contain a variety of fraction sizes to ensure adequate compaction of coarse aggregate particles, thus resulting in increased density and lower voids in the concrete.
Once the appropriate materials are determined, now we can make concrete objects in the molds we want using concrete mortar. The materials required for a concrete object are calcium aluminate cement, aggregate suitable for the size of the mold, water, and chemical additives. Some paraffin oil should be applied to the inside of the molds that will come into contact with concrete. Thus, the concrete comes out of the mold more easily.
After putting the ingredients in a bowl, they should be mixed. It is best to use high strength concrete for better results. The calcium aluminate system requires an accelerator to reduce hardening times. Lithium carbonate (LiCO3) can be used for this purpose. Lithium carbonate is an active hardening accelerator preferred in cements used in the construction industry to accelerate freezing and increase early strength development. Thus, rapid freezing is ensured, which saves time and application according to the area of use for the cement. Besides, a set retarder can be additionally used in this system to manage workability. The hardening accelerator and set retarder additives that can be used in calcium aluminate cement are presented in Table 1 below.
Table 1. Hardening time adjusting regulators used with CAC
You can also add glass shards, stones, shells, pearls, or other decorative items in concrete mixture.
Examples of Making Concrete Objects with Calcium Aluminate Cement
Please check out this title to see beautiful concrete decorations you may use in your home.
Figure 2. Concrete Objects
Figure 3. Concrete Objects
Things You Need to Know About Making Concrete Objects with Calcium Aluminate Cement
This article was about how we can make concrete objects using calcium aluminate cement. It is important to make durable concrete for long-term use. In addition to cement, aggregates and additives also matter. Moreover, the water-cement ratio should be kept below 0.4 and mechanical vibration should be used to place the concrete. Calcium aluminate concretes generate heat much faster than Portland cement concrete, and good curing is required for 24 hours after placement for the desired strength gain.
References:
- Peter Hewlett, M. L. (2019). Lea’s Chemistry of Cement and Concrete. Elsevier.
- Calcium Aluminate Cement: Issues to Take into Consideration
