Introduction:
The thickness of cement concrete pavement is designed to withstand various types of stresses it will experience during its service life. The most significant stresses that affect pavement performance include temperature stresses, load stresses, friction stresses, and their combinations. Among these, the design thickness of cement concrete pavement is primarily based on load plus temperature stresses.

Load Stresses:
- Load stresses refer to the forces exerted on the pavement due to the weight of vehicles and their loads.
- The thickness of the pavement needs to be sufficient to distribute these loads over a larger area, minimizing the stresses transmitted to the underlying layers and subgrade.
- The design thickness for load stresses is determined based on the anticipated traffic volume, vehicle types, and axle loads.

Temperature Stresses:
- Temperature stresses are caused by the expansion and contraction of the concrete pavement due to temperature variations.
- As the temperature changes, the concrete expands or contracts, leading to thermal stresses that can cause cracking and deformation.
- The design thickness for temperature stresses is determined based on the coefficient of thermal expansion of concrete, the temperature range expected in the region, and the restraint provided by the surrounding structures.

Load Plus Temperature Stresses:
- Load plus temperature stresses consider the combined effect of both load and temperature variations on the pavement.
- The load stresses and temperature stresses act simultaneously and can have a cumulative effect on the pavement's performance.
- Designing the thickness of the pavement to withstand load plus temperature stresses ensures its structural integrity and longevity.

Load Plus Friction Stresses:
- Friction stresses occur due to the interaction between the pavement surface and the tires of moving vehicles.
- Friction stresses can cause abrasion and wear of the pavement surface, leading to reduced skid resistance and durability.
- While friction stresses are important considerations, they are not the primary factor in determining the thickness of cement concrete pavement.

Conclusion:
The design thickness of cement concrete pavement is primarily based on load plus temperature stresses as they are the most critical factors affecting pavement performance. While other stresses such as load plus friction stresses are considered, they do not have as significant an impact on the pavement's overall thickness design. By considering load plus temperature stresses, engineers can ensure that the pavement is adequately designed to withstand the anticipated traffic loads and temperature variations, providing a durable and long-lasting infrastructure.