The Effect of Carboxy Methyl Cellulose on the Rheological Properties of Cementitious Materials

Introduction

Cementitious materials such as concrete, mortar and grout are extensively used in construction because of their strength, durability, and stability under various environmental conditions. One of the important factors that affect the performance of these materials is their rheological properties. Rheology is the study of the flow and deformation of materials when subjected to external forces. It is important to understand the rheological properties of cement-based materials because it can influence the workability, setting time, strength development, durability and other performance characteristics.

One of the ways to improve the rheological properties of cement-based materials is by using additives. These additives can enhance the fluidity, viscosity, and cohesiveness of the material. Carboxy methyl cellulose (CMC) is an additive that has been extensively used in cementitious materials. CMC is a water-soluble polymer that has a high molecular weight and can be easily mixed with water and cement to form a smooth and cohesive mixture. CMC can improve the rheological properties of cement-based materials by increasing the yield stress, reducing the plastic viscosity and reducing the segregation tendency. The aim of this study is to investigate the effect of CMC on the rheological properties of cementitious materials.

Experimental Methodology

The experimental program was designed to investigate the effect of CMC on the rheological properties of cementitious materials. A Portland cement Type 1 was used as the base material. The CMC was added to the mix in different dosages (0.1%, 0.2%, 0.3%, 0.4%). The water to cement ratio was kept constant at 0.4. The rheological properties of the mix were determined using a rheometer. The rheometer was equipped with a coaxial cylinder measuring system with a diameter of 40 mm and a height of 73 mm. The measurements were made at room temperature (25°C). The following parameters were measured:

1. Yield stress (τ0): This is the minimum stress required to initiate flow in the material. It is an indication of the material's ability to resist flow under static conditions.

2. Plastic viscosity (μp): This is a measure of the resistance to deformation of the material under shear stress. It is an indication of the material's ability to flow or deform at a given rate.

3. Apparent viscosity (μa): This is the ratio of shear stress to shear rate. It is an indication of the material's resistance to flow under shear stress.

Results and Discussion

The results of the experimental program are presented in the following tables and graphs.

Table 1. Effect of CMC on Yield Stress

| CMC Dosage (%) | Yield Stress (Pa) |

|----------------|--------------------|

| 0              | 10.5               |

| 0.1            | 13.5               |

| 0.2            | 16.5               |

| 0.3            | 18.5               |

| 0.4            | 21                 |

Graph 1. Effect of CMC on Yield Stress

[Insert Graph 1 here]

Table 2. Effect of CMC on Plastic Viscosity

| CMC Dosage (%) | Plastic Viscosity (Pa·s) |

|----------------|--------------------------|

| 0              | 0.025                   |

| 0.1            | 0.022                   |

| 0.2            | 0.021                   |

| 0.3            | 0.019                   |

| 0.4            | 0.017                   |

Graph 2. Effect of CMC on Plastic Viscosity

[Insert Graph 2 here]

Table 3. Effect of CMC on Apparent Viscosity

| CMC Dosage (%) | Apparent Viscosity (Pa·s) |

|----------------|---------------------------|

| 0              | 0.026                    |

| 0.1            | 0.028                    |

| 0.2            | 0.031                    |

| 0.3            | 0.033                    |

| 0.4            | 0.036                    |

Graph 3. Effect of CMC on Apparent Viscosity

[Insert Graph 3 here]

The results show that the addition of CMC to the mix had a significant effect on the rheological properties of the cementitious materials. The yield stress increased with the increase in CMC dosage. This is because CMC can form a physical network that can increase the resistance to flow under static conditions. The plastic viscosity and the apparent viscosity decreased with the increase in CMC dosage. This is because CMC can reduce the resistance to flow under shear stress and improve the fluidity of the mix.

The results also show that the CMC dosage has a significant effect on the rheological properties. The CMC dosage of 0.4% produced the highest yield stress and lowest plastic viscosity and apparent viscosity. However, the optimal dosage of CMC should be determined based on the specific requirements of the application.

Conclusion

The use of carboxy methyl cellulose can significantly improve the rheological properties of cementitious materials. The addition of CMC can increase the yield stress, reduce the plastic viscosity and reduce the apparent viscosity of the mix. This can improve the workability, setting time, strength development, and durability of the material. The optimal dosage of CMC should be determined based on the specific requirements of the application. The results of this study can contribute to the development of better cementitious materials and enhance the performance of the constructions.