During the long period of high cement demand growth rates in the late 1990s and early 2000s, the South African cement industry had little incentive to formulate specialist products for the road construction sector. However, with the commissioning in 2009 of its grinding station, in Randfontein, cement manufacturer Lafarge Cement says it had the available capacity to introduce new products and develop new market sectors.

 

Lafarge Cement, the wholly owned subsidiary of building materials manufacturer Lafarge, notes that the South African National Roads Agency Limited (Sanral) was starting to tackle the large backlog of maintenance and rehabilitation on provincial and municipal roads and, recognising the potential, Lafarge Cement used its technical resources to develop its new road binding cement, RoadCem.

Produced at the company’s Randfontein grinding station, RoadCem is another addition to the company’s range of lower- carbon footprint cements.

Developed specifically as a road binding material in cooperation with major road contractors, RoadCem is a CEM II 32.5 N cement formulated from Portland cement, siliceous fly ash and blast furnace slag.

It is designed to provide a solution for improving the engineering properties of soil by reducing the plasticity index, while also improving the unconfined compressive strength and initial tensile strength.

The company says the product modifies clay minerals and achieves increased soil strength and bearing capacity, as well as better volume stability, by controlling the swell and shrinkage characteristics caused by moisture changes. This also enhances resistance to erosion, weathering or traffic loading.

The principal road stabilisation products used are lime, Portland cement, fly ash, slag or mixtures of these to address the specific site conditions and conform to the applicable standards.

Cement is effective in stabil- ising a wide range of soils including granular materials, silts and light clays. A particular advantage of cement is its capability of being used in conjunction with by-products such as fly ash and slag, says Lafarge Cement.

Cement is composed of calcium silicates and calcium aluminates that hydrate when combined with water to form the cementing compounds of calcium silicate hydrate and calcium aluminate hydrate. The reaction also releases calcium hydroxide.

 

The company adds that the formation of the cementitious products and calcium hydroxide make Portland cement successful in stabilising both granular and fine-grained soils, as well as aggregates and miscellaneous materials.

In fine-grained clay soils, a reaction between the calcium hydroxide released during hydration and the alumina and silica in the soils, is an important factor in the stabilisation of these clay soils.

The permeability of cement stabilised soil is greatly reduced, resulting in a moisture-resistant material that is highly durable and resistant to leaching over the long term.

 

Cement sold in South Africa must comply with SANS 50197-1: 2000 and EN 197-1.

“In the absence of a specific local standard for road stabilisation, compliance with the European Standard (ENV 13282) is recommended.”

“Key mechanical requirements are strength classes of 12.5 MPa to 32.5 MPa. Materials used in stabilised layers are required to conform to the requirements specified in the Standard Speci-fication (COLTO, 1998) or the specifications in the particu- lar project,” says Lafarge head of Quality Department Southern Africa Dr Reinhold Amtsbüchler.

He adds that the roadbinding cement product needs of road construction contractor cus- tomers can be summarised as a superior performance cement that offers the characteristics of a slow setting cementitious binder; extended working time; a reduction in plasticity index; suitability for different soil conditions; long- term strength and workability.

 

RoadCem achieves strengths of 16 MPa at one week and 32.5 MPa at four weeks, as required for this class of general purpose cement in accordance with the regulated standard SANS 50197-1:2000 and EN 197-1.

Lafarge notes that the product is particularly suitable for stabilisation of road base, sub-base and sub-grade materials; soils with either low or moderate plasticity – especially granular- type materials with a lower plasticity index and in situ (including deep lift) stabilisation or pugmill blending.

 

Product Success

 

Amtsbüchler says demand for RoadCem for soil stabilisation is increasing on major road refurbishment and upgrading projects.

“These projects include 46km of the N8 between Ladybrand and Tweespruit, in the Free State, as well as sections 2 and 3 of the Bakwena N4 toll road upgrade between Brits and Rustenburg,” he says.