Mortar and Epoxy Systems: Repair and Construction Solutions

Posted on Aug 20, 2024 in Physics

Mortars with Polymers

Cement mortars with added acrylic polymer or synthetic latex emulsions are known as polymer mortars. These emulsions are typically made from three types of polymers:

  • Acrylics
  • Styrene-butadiene rubber (SBR)
  • Polyvinyl acetate (PVA)

Polymer emulsions are used in two main applications:

Grout Adhesive

Grout adhesive acts as a bonding bridge between fresh mortar and concrete or masonry bases. To prepare the grout, mix cement bond and fine sand in a 1:1 ratio. Then, add acrylic emulsion diluted with water according to the manufacturer’s instructions, mixing until creamy. Apply the slurry with a brush to the surface. The mortar must be applied within an hour of mixing.

Mortars with Polymers

Adding acrylic emulsion to cement mortars significantly improves several properties:

  • High adhesion to the base (resistance to cutting at 28 days is at least 5 Kgf/cm2)
  • Compressive strength after 28 days: 250 to 450 Kgf/cm2
  • Flexo traction resistance after 28 days: 65 to 100 Kgf/cm2
  • Compression modulus: 250,000 Kgf/cm2
  • Low wing cracking tendency

The recommended dosage is 1:3 to 1:3.5 (by weight) with a water-cement ratio between 0.30 and 0.40 (including acrylic emulsion previously dissolved in water).

Mortars with polymers are primarily used for repair work and thin-layer applications.

Dosing Mortars

Several pre-prepared products are available on the market, either ready-to-use or requiring only the addition of water. These products offer advantages such as:

  • Controlled manufacturing
  • Precise dosing
  • Specific purpose design
  • Suitable for repair work where quality is critical and/or control is limited

Types of Dosing Mortars

  • Repair mortar: Low shrinkage, controlled shrinkage, and/or ripple effect.
  • Fast-set mortar: High-speed tightening for quick jobs.
  • Thixotropic mortars: Consistent enough to work vertically and overhead without dripping.
  • Screed mortar: Fluid, for applying to elements or horizontal surfaces (floors).
  • Grout or filled mortars: Generally expansive fluids for injections and fillers, suitable for tight spaces.

Properties of Dosing Mortars

Specific properties vary between products and manufacturers. Generally, they are characterized by:

  • High resistance (over 300 Kgf/cm2)
  • Rapid development of resistance
  • Good adhesion to concrete and masonry
  • Low shrinkage

Epoxy Systems

Epoxy systems are synthetic products that harden through a chemical reaction between a resin and a hardener. Common formulations include different types of hardeners, modifiers, solvents, and mineral fillers as needed. They are delivered in 2 or 3 components:

  • Part””: Resin
  • Part””: Hardener
  • Part””: Aggregate filler

Dosages

Carefully prepare the resin-hardener proportion (A:B) as indicated by the manufacturer. In most cases, complete sets are used with pre-determined dosages. The proportion of part”” filler can be adjusted based on the required properties and consistency of the work.

Depending on the application, epoxy systems can be used as:

  • More or less viscous liquids, depending on the formulation.
  • Thick consistency pastes, with added quartz powder and potentially a thixotropic agent.
  • Epoxy mortar: Adding a blend of resin-hardener sand, usually quartz, with a specific size distribution. The ratio of hardener and resin to sand is between 1:1 and 1:10 by weight. A + B / C = 1:1 to 1:10.

Viscosity

The viscosity of pure epoxy systems (without filler) can range between 100 and 2500 centipoise (cps) at 20°C, depending on the formulation. Viscosity can be increased with fillers to form thixotropic pastes. Conversely, for injection work, low-viscosity products are needed.

Retraction Speed

Retraction speed determines the pot life or initial setting time and the development of resistance to tightening deadlines. It depends on the formulation, temperature, and volume of the mixture. Generally, high resistance is achieved at an early age, allowing for commissioning within the first three days. The reactions are exothermic, which may limit the volumes that can be prepared.

Retraction

Hardening occurs with virtually no shrinkage.

Mechanical Properties

:
· Compressive strength: 400 to 1000 Kgf/cm2 at 7 days
· Flexo traction resistance: 200 to 800 Kgf/cm2 at 7 days.
· Adhesion to steel: over 200 Kgf/cm2
· Adhesion to concrete: 50 Kgf/cm2 rupture of concrete.
· Modulus of Elasticity: 10,000 to 350,000 according Kgf/cm2 formulation and content of filler
· Thermal sensitivity: the application temperature influences the viscosity and velocity.