By Carl White
Africa faces unique construction challenges. These include sulphate-rich soils and groundwater in mining areas, coastal chlorides, variable quality aggregates, high cement costs, logistics issues in remote regions, and a strong push for sustainable and affordable durable infrastructure.
Spray-Lock Concrete Protection (SCP) offers a practical, durable alternative to silica fume for sulphate-resistant concrete, delivering strong benefits in ease of use, cost, and logistics across the African continent.
Post-Applied Colloidal Silica
Post-applied colloidal silica (nano-scale or colloidal nano-silica) enhances both new and existing concrete. Primarily, it optimises water usage, significantly reduces permeability, and improves overall durability by promoting additional calcium silicate hydrate (C-S-H) formation within the concrete matrix.
In contrast, silica fume (micro-silica) is a traditional pozzolanic supplementary cementitious material (SCM) added as a dry powder. It is renowned for its ultra-fine particles that react with calcium hydroxide (CH) to form extra C-S-H, densifying the matrix, lowering permeability, and boosting resistance to sulphate attack, chlorides, and other aggressive agents.
Same or Greater C-S-H boost
In many cases, SCP can improve – or at least match – durability in sulphate-resistant concrete applications.
Testing with SCP products use an ordinary portland cement paste without silica fume or fly ash which would assist in increasing the concrete durability results.
Both promote additional calcium silicate hydrate (C-S-H) formation, which refines the pore structure, sharply reducing permeability, and limiting ingress of sulphates, chlorides, and other ions.
SCP leverages colloidal silica technology to penetrate deeply and react within the matrix, disconnecting capillaries and blocking fluid movement. Research on colloidal nano-silica shows it can provide comparable or superior reductions in sulphate-related expansion. In some studies, colloidal forms reduced expansion more effectively at lower dosages than silica fume equivalents, with strong resistance to combined chloride-sulphate attacks.
Colloidal silica treatments are documented to enhance resistance to sulphate attack, chemical ingress, salt penetration, and aggressive environments overall. This complements sulphate-resistant Portland cement (Type II or V equivalents, or blended cements) by emphasising low permeability to prevent ettringite/gypsum formation and expansion. Independent testing and industry reports highlight colloidal silica’s ability to improve durability against sulphate exposure, often with benefits in reduced mass loss, lower porosity increase, and maintained strength under long-term immersion.
… with Logistics and Cost Wins
However, silica fume has notable practical drawbacks:
- Its dry powder form, which is difficult to handle, dusty, requires high-shear mixing, and can lead to reduced workability if incorrectly dosed.
- Higher risk of balling or inconsistent dispersion in the mix.
- Often more expensive and logistically challenging in remote or high-volume sites, requiring special storage/silos and increasing transport costs in sub-Saharan Africa.
SCP directly addresses these, providing:
- Easier logistics and handling. Its liquid form suits sites with limited equipment for dust control or specialised mixing, mitigating dust hazards and simplifying batching in remote or resource-constrained areas.
- Cost-effectiveness by optimising water use, enabling lower cement content (reducing material costs), and improving long-term durability. This leads to extended service life and fewer repairs in budget-constrained public works and infrastructure projects.
- Supply security in Africa, where blended cements with fly ash/slag are common for sulphate resistance, SCP enhances mixes without relying on imported dry silica fume (which can be expensive, scarce, or delayed by supply chain disruptions).
Sustainability Alignment
Furthermore, pozzolanic enhancement supports partial cement reduction, significantly lowering the CO₂ footprint of concrete mixes. This aligns closely with accelerating ESG (Environmental, Social, and Governance) trends across Africa. Construction and cement sectors face mounting pressure to decarbonise amid rapid urbanisation and massive future build-out – 80% of Africa’s 2050 building stock is yet to be constructed, driving a projected 230% surge in cement demand by mid-century.
White is the Managing Director of Spraylock Africa, which is Future Proofing Concrete through innovative colloidal silica technology
