Manufacturing mechanism of paraffin oil emulsion-red clay-coal ash composite waterproof agent

Statement of the problem. Waterproofing of cement-based structures is a critical challenge in construction, particularly in moisture-prone environments. Traditional methods often rely on expensive polymer-based admixtures or surface treatments, which can be cost-prohibitive for large-scale projects and offer limited durability. The primary pathway for water infiltration is through capillary pores (> 10,000 Å) within the cement matrix. This study addresses the need for a cost-effective, high-performance waterproofing solution by developing a composite admixture that combines the hydrophobic properties of paraffin oil emulsion with the pore-filling capabilities of industrial waste materials (red clay and coal ash). Results. Through systematic experimental design and optimization, the optimal formulation was determined as 7 % paraffin oil emulsion (solid basis) combined with a red clay-coal ash mixture at a 1:1 mass ratio to paraffin solids. The composite admixture delivers exceptional waterproofing performance, achieving a 28-day capillary absorption rate of only 1.21 % — representing a dramatic 69 % reduction compared to plain mortar (3.90 %). Microstructural analysis confirmed a dual-mechanism effect: sub-micron paraffin droplets (<i>d</i>₅₀ = 2.8 µm) physically coat pore walls, creating hydrophobic surfaces (contact angle >110°), while the red clay-coal ash undergoes pozzolanic reactions, consuming ~30% of portlandite and generating additional calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) phases that refine capillary pores from 0.18 to 0.11 mL/g. The formulation maintains structural integrity with a compressive strength of 19.5 MPa, equivalent to the control specimen. Conclusions. The paraffin oil emulsion-red clay-coal ash composite represents an efficient, economical, and environmentally friendly waterproofing solution. It successfully balances high-performance water repellency with preserved mechanical strength, offering an 82—88 % cost reduction compared to commercial crystalline admixtures at a final production cost of USD 1.46/kg. The utilization of industrial waste materials contributes to sustainable construction practices, while the exceptional cost-performance ratio makes it a highly viable alternative to conventional waterproofing technologies.