Repair Systems — 02 — Concrete & Structural Defects
Cement and aggregates for site-batched repair mortars
Technical product reference for GP Portland cement, supplementary cementitious materials (fly ash, silica fume), and washed fine aggregates used in site-batched cementitious repair mortars for concrete spalling repair. Covers material selection, mix design principles, and Australian standards compliance under AS 3972 and AS 3582.
Cement and aggregates in concrete spalling repair
Cement and aggregates are listed as a product category for concrete spalling repair because they are sometimes needed for site-batched mortars, bonding slurries, and structural reinstatement concrete. However, the primary recommendation for concrete spalling repair in Australian remedial practice is to use factory-manufactured pre-bagged polymer-modified repair mortars (such as Sika MonoTop, Ardex BR series, Fosroc Renderoc, or Mapei Mapegrout) rather than site-batching from raw cement and aggregate.
Product Reference
Individual products — one card each — scroll to view all
Boral / Holcim / Adbri
General Purpose (GP) Portland Cement — 20 kg
GP Portland cement — AS 3972 Type GP — bagged 20 kg
General Purpose (GP) Portland cement to AS 3972 is the standard cement used in site-batched repair mortars, bonding slurry, and concrete used in concrete spalling repair. It is used as the primary cementitious binder when the repair is batched on-site from raw materials — for example, a repair mortar mix proportioned as 1 part GP cement : 3 parts washed concrete sand : SBR latex admixture. For remedial work, bagged 20 kg GP cement from Boral, Holcim, or Adbri is the most practical supply form for small-volume site batching.
Flyash Australia / Holcim / Regional
Fly Ash — Supplementary Cementitious Material (SCM)
Fly ash — Class F — AS 3582.1 — supplementary cementitious material
Class F fly ash to AS 3582.1 is a supplementary cementitious material (SCM) added to site-batched repair mortars and concrete to improve workability, reduce permeability, and increase long-term durability — particularly in chloride and sulfate-exposed environments. Fly ash is a by-product of coal combustion collected as fine particulate from power station exhausts. In remedial repair mortar, fly ash is typically added at 20–30% of total cementitious content as a partial replacement for GP cement.
Elkem / Local Suppliers
Silica Fume (Microsilica) — Densified
Silica fume — densified — AS 3582.3 — high-durability SCM
Densified silica fume (microsilica) to AS 3582.3 is a highly reactive pozzolanic SCM added to site-batched repair mortars and concrete at 5–10% of total cementitious content to dramatically reduce permeability and chloride ion penetration. Silica fume particles are approximately 100 times finer than GP cement — they fill the microscopic voids between cement particles in the hydrated paste, creating a very dense, low-permeability matrix. This is particularly valuable in chloride-affected spalling repair on coastal structures, marine structures, and carpark decks exposed to de-icing salts or sea spray.
Boral / Independent Quarries
Washed Concrete Sand and 10 mm Crushed Aggregate
Fine and coarse aggregate — AS 2758.1 — site-batched repair mortar
Washed concrete sand (fine aggregate, particle size 0–5 mm, zone M or zone C) and 10 mm crushed coarse aggregate to AS 2758.1 are used in site-batched repair mortars and concrete for concrete spalling reinstatement repair. Washed concrete sand is the fine aggregate component in site-batched repair mortars — it must be clean, washed, free of organic material, clay, and salt contamination. Contaminated or dirty sand significantly reduces mortar strength and increases shrinkage.
System Comparison
Concrete spalling — confirm all selections against the current manufacturer TDS before specifying.
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Do not confuse cement and aggregates for repair mortars with:
- Pre-bagged polymer-modified repair mortars (Sika MonoTop, Ardex FC 12, Fosroc Renderoc, Mapei Mapegrout) — these are factory-proportioned repair systems with calibrated polymer content, admixtures, and graded aggregates — more consistent and easier to apply than site-batched mortars from raw materials — listed on the repair mortars (PM) page
- Concrete mix for structural pours — ready-mix concrete specified to AS 1379 (normal or special class) is a different product from site-batched repair mortar — used for large volume reinstatement pours, not small patch repairs
- GP cement as a self-standing repair product — GP cement mixed with water alone (without aggregate and polymer admixture) produces a weak, high-shrinkage paste that is not suitable as a concrete repair mortar — always follow an engineered mix design when using raw materials
- Rapid-set cement blends (e.g. Rapid Set Cement All, Holcim ProCem) — these are calcium sulfoaluminate or proprietary rapid-set cements, not standard GP Portland cement — they have very different setting times, strengths, and mix design requirements
- Refractory and high-temperature mortars — calcium aluminate cements and refractory aggregates used in high-temperature applications are not the same as GP Portland cement mixes and are not suitable for standard concrete spalling repair
Disclaimer
This page provides general technical information only. Final product selection must be confirmed against the current manufacturer technical data sheet, project specification, substrate condition, exposure classification, AS 3600 requirements, and applicator warranty conditions. Do not rely on this reference as a substitute for professional engineering or remedial building consultant advice.