GRT Launch Polymer Modified Cement

Based on the proven use of polymers in specialised structural concrete, GRT have developed polymers to be used in pozzolanic stabilisation of pavement materials.

The goal was to overcome the shortcomings and improve properties of using cementitious materials alone. Polymer modified cement created by Global Road Technology is a combination of cementitious binder, GRT polymer, water and granular material. These components are mixed together and compacted in the early stages of the hydration process to form a pavement layer that is subsequently cured.

Hardened conventional cement paste has mainly an agglomerated structure of calcium silicate hydrates and calcium hydroxide bound together by the weak intermolecular forces. Consequently, microcracks occur easily in the cured material under stress. That is why ordinary cement mortar and concrete have poor tensile strength and fracture toughness. On the other side, in the polymer modified cement, it appears that the microcracks are bridged by the polymer films which prevent crack propagation, and simultaneously, a strong cement hydrate-aggregate bond is developed. Polymer membranes also add sealing effect to the formed structure and thus provide a considerable increase in waterproofness or watertightness, resistance to chloride ion penetration, moisture transmission, carbonation and oxygen diffusion, chemical resistance and freeze-thaw durability. Depending on traffic volumes and environmental conditions at the time, GRT polymer modified cement blend pavements can generally be trafficked immediately after final compaction.

Summarized processes for creation of polymer modified cement are as follows: After mixing with water, the cement paste particles start to hydrate and cement gel gradually forms on the surface of the cement particles. The unhydrated cement particles covered with cement gel is being enveloped with a closely packed layer of introduced polymer particles. The water removes by cement hydration and evaporation, and the closely packed polymer particles, positioned on the cement hydrates, integrate into continuous membranes. The membranes bind the cement hydrates together to form a monolithic network.

The binder should be added in sufficient quantity to balance both strength and shrinkage requirements to produce a bound material with significant tensile strength.  In most cases, cementitious contents for GRT polymer mix designs are limited to 2 to 3%.

Advantages of GRT polymer modified cement when compared to conventional cement stabilised or treated pavements include:

• Significantly reduced or eliminated shrinkage cracking
• Rapid curing at ambient temperatures
• Higher tensile, flexural, and compressive strengths for the same cement content
• Improved vibration dampening
• Improved adhesion to most surfacings
• Improved long-term durability with respect to freeze and thaw cycles
• Lower permeability to water and aggressive solutions
• Improved chemical resistance
• Improved workability i.e. requires less compactive effort for a given depth of compaction and can be compacted in greater single lifts

Due to its advanced properties GRT polymer modified cement has numerous potential applications:

• Rehabilitation and strengthening of existing granular pavements;
• Recycling of existing cement stabilized pavements which are exhibiting extensive shrinkage cracking;
• Construction of pavements and/or working platforms in limited or constrained construction times;
•   In areas susceptible to high rainfall or inundation;
• Over soft ground conditions where stiff bridging layers are required to compact overlying materials;
• Where temporary trafficking of the pavement may be required during different stages of construction;
• When preferred maximising of use of local materials and for making marginal pavement gravels suitable for purpose;
• Modification or improvement of non-organic subgrade conditions;
• Where construction water availability is limited as GRT polymer modified cement reduces construction water requirements and depending on the water quality may enable the use of non-potable water.

For more information regarding Global Road Technology or GRT Polymer Modified Cement please contact GRT.