Use of Setting Accelerators in Cement-Based Mortars

Setting accelerators increase the degree of hydration of the substance, enabling it to set in a shorter time. Setting accelerators can belong to very different categories of compounds.

The substances used here are;

• Lithium Carbonate
• Sodium Carbonate
• A mixture of Lithium Carbonate and Sodium Carbonate

It is important to ensure rapid setting, especially when pouring concrete in cold weather conditions. At the same time, it must not have a corrosive effect and must provide the properties of other additives. For this, a freezing point depressing organic salt can be used.

As a result of using these substances, changes in the following properties were examined.

• Workability
• Amount of Entrapped Air
• Setting Time
• Dynamic Modulus of Elasticity
• Compressive Strength
• Shrinkage
• Water Absorption Capacity
• Carbonation Rates

To retard the setting in the initial mortar system, Tartaric Acid is used. The usage rate here is approximately 0.80%.

What are the Effects of Using Lithium Carbonate and Sodium Carbonate?

In processes using Lithium Carbonate and Sodium Carbonate, high levels of air entrapment do not occur. Furthermore, it has been determined that the use of Lithium Carbonate and Sodium Carbonate has different effects on the resulting mortar consistency.

The workability is better in the product to which Sodium Carbonate and Sodium Carbonate-Lithium Carbonate mixtures are added, and an improvement was observed. However, in applications using lithium carbonate, no change in workability was observed.

Additionally, the use of lithium carbonate causes a significant reduction in the pot life of the mortar.

When Lithium Carbonate is used, the effect of Tartaric Acid, which is used for its retarding effect, is completely nullified. It reduces the pot life to 30 minutes. In applications using Sodium Carbonate, the pot life experienced only a slight decrease. The combination of Sodium Carbonate and Lithium Carbonate mixture caused a reduction of about 30% in pot life.

Effects on Porosity

The porosity in studies using Sodium Carbonate is greater than in the formula using Lithium Carbonate. In other words, sodium carbonate applications result in finer pores.

Compressive Strength

The compressive strength of materials using Lithium Carbonate and Sodium Carbonate was tested, and it was found to have a positive effect.

Additionally, the addition of Lithium Carbonate accelerates the hydration process within the system.

Shrinkage

Sustainable mortars exhibit a certain level of traditional shrinkage. The addition of certain hardening and accelerating substances has profound effects on shrinkage.

Lithium Carbonate and mixtures of Lithium and Sodium Carbonate caused a 100% increase in shrinkage.

Water Absorption Capacity

Materials containing Sodium Carbonate exhibit a 25% lower water absorption capacity compared to those with Lithium Carbonate and additive-free mortars.

Carbonation Effect

The addition of Lithium Carbonate and Sodium Carbonate helps to refine the pore structure. This facilitates carbon dioxide penetration. The greatest reduction in carbonation tendency (60%) is observed in mortars with added Sodium Carbonate.

Use of Sodium Carbonate in Cement Mortar Preparation:

In this application, sodium carbonate is used to reduce air bubbles, retard the setting (solidification) time, increase freeze-thaw resistance, and enhance water resistance. It must be dissolved in water before being added to the cement mortar.