Evaluation of Admixture Silane Added into Cementitious Pastes

Area of Science:

• Materials Science
• Civil Engineering
• Chemical Engineering

Background:

• Superplasticizers are crucial for enhancing the workability of cementitious materials.
• Silanes are being explored as potential additives in cementitious matrices.
• Understanding the performance of silanes as partial replacements for superplasticizers is essential for developing advanced concrete technologies.

Purpose of the Study:

• To evaluate the performance of three distinct silanes (VTES, AEAPTMS, MCPTMS) as partial replacements for polycarboxylate ester-based superplasticizers in Portland cement pastes.
• To assess the impact of varying substitution levels (20% and 40%) of silanes on the fresh and hardened properties of cement pastes.
• To analyze the hydration kinetics and mechanical performance of cementitious matrices modified with silanes.

Main Methods:

• Preparation of cement pastes with a water/cement ratio of 0.186.
• Partial substitution of superplasticizer with vinyltriethoxysilane (VTES), n-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPTMS), and methacryloxypropyltrimethoxysilane (MCPTMS) at 20% and 40% levels.
• Evaluation of fresh properties: specific gravity, trapped air, mini-slump, and isothermal calorimetry for hydration kinetics.
• Assessment of hardened properties: compressive strength, flexural strength, specific gravity, and absorption by immersion at 7 and 28 days.

Main Results:

• VTES and AEAPTMS significantly reduced workability and increased air content at both substitution levels.
• MCPTMS showed minimal impact on workability and air content.
• All silane-modified pastes exhibited delayed hydration kinetics compared to the reference.
• Flexural strength decreased with all silane substitutions.
• Compressive strength decreased, except for MCPTMS, which showed comparable or improved strength at 7 and 28 days.
• All samples displayed high absorption and void index values.

Conclusions:

• Methacryloxypropyltrimethoxysilane (MCPTMS) demonstrates potential as a partial superplasticizer replacement in cement pastes due to its limited negative impact on workability and its ability to maintain compressive strength.
• Vinyltriethoxysilane (VTES) and n-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPTMS) negatively affect workability and strength, limiting their applicability.
• Further research is needed to optimize silane usage and mitigate negative effects on absorption and void content in cementitious materials.