Banca de DEFESA: LAISA DO ROSARIO SOUZA CARNEIRO

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : LAISA DO ROSARIO SOUZA CARNEIRO
DATE: 15/02/2024
TIME: 14:00
LOCAL: https://conferenciaweb.rnp.br/sala/peter-ludvig
TITLE:

ADDITIONS AND COATINGS OF HIBRID SILICAS SINTHESIZED VIA SOL-GEL PROCESS FOR THE DEVELOPMENT OF HYDROPHOBIC CEMENTITIOUS COMPOSITES AIMING THE ENHANCEMENT OF LIFE SPAN AND DURABILITY OF STRUCTURES

KEY WORDS:

hybrid sol-gel silica; hydrophobicity; sol-gel process; durability;mechanical properties

PAGES: 162
BIG AREA: Engenharias
AREA: Engenharia Civil
SUMMARY:

The issues related to the durability of buildings are usually associated with the presence of moisture or water infiltration through the pores of the cementitious materials composing the structures. Advances in biomimetics and nanotechnology have enabled the development of hydrophobic and superhydrophobic materials capable of repelling water at angles 150º, respectively. The synthesis of these materials often involves the combination of a low surface energy material (such as alkylsilanes, siloxanes, etc.) with an appropriate surface microroughness. This study aimed to synthesize hybrid silicas through the sol-gel technique and apply them directly as coatings and additives in cement pastes and mortars. The synthesis utilized the silane precursors trimethoxymethylsilane (MTMS), isobutyl(trimethoxy)silane (IBTES, and triethoxy(octyl)silane (OTES), which have a hydrophobic organic branch that repels water. The properties of the coated and addition-containing samples were evaluated over time and under various environmental conditions through durability tests, hydrophobicity assessments, and mechanical tests. Samples with 6% addition of MTMS hybrid silica exhibited a capillary absorption 40.5% lower than the reference sample. However, mechanical resistance was compromised, being about 30% lower. Samples coated with hybrid silica exhibited contact angles up to 109º (cement pastes) and 127º (mortars) and absorbed up to 136 times less water via capillary pores than the reference sample. The organic chain length of the hybrid precursors and the substrate surface micro-roughness directly influenced the hydrophobic and the durability properties of the coated cementitious materials. The best results were obtained in the coating with the longest aliphatic chain (8 carbon atoms), made from triethoxy(octyl)silane (OTES), which was applied in mortars. This coating was also the most effective over time (90 days) and under different environmental conditions. The most effective and durable coatings are ranked as follows: OTES-based silica > IBTES-based silica > MTMS-based silica. The carbonation depth in mortars coated with IBTES-based and OTES-based silicas were smaller at 270 days of exposure than carbonation depth of the reference sample at 90 days.

COMMITTEE MEMBERS:
Presidente - PETER LUDVIG
Interno - AUGUSTO CESAR DA SILVA BEZERRA
Externo à Instituição - MANUEL HOUMARD - UFMG
Externo à Instituição - FERNANDO DO COUTO ROSA ALMEIDA - UFMG
Externo à Instituição - FERNANDO PELISSER - UFSC