Banca de DEFESA: VITOR ALENCAR NUNES

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : VITOR ALENCAR NUNES
DATE: 30/10/2023
TIME: 09:00
LOCAL: Belo Horizonte (remoto)
TITLE:

Feasibility of steel slag as binder and aggregate in alkali activated materials

KEY WORDS:

steel slag, waste recycling, alkali-activated materials, activation parameters, pretreatment

process, volume stability.

 

PAGES: 166
BIG AREA: Engenharias
AREA: Engenharia Civil
SUBÁREA: Construção Civil
SPECIALTY: Materiais e Componentes de Construção
SUMMARY:

Steel slag (SS) is a solid waste generated during the steelmaking process, with annual generation of 270

million tons of SS worldwide. SS can be reused as an alternative raw material in several applications due

to its chemical composition, mechanical and physical properties: in agriculture, soil stabilization, road

construction and other building materials. However, the recovery rate for SS varies from 20 to 98%,

depending on the country, which leads to an excessive stockpiling causing environmental harm and

financial liability. So far, considerable quantities of SS are employed in road construction and internal

recycling (steel making) but still with many restrictions. The construction sector appears as a potential

consumer of large quantities of SS. However, the volumetric instability of SS may be an issue for

application in Portland cement (PC) based products. An alternative reuse for the SS would be as raw

material in the alkali-activated materials (AAM). AAM are alternative materials that could present better

mechanical and durability performances; they also incorporate larger amounts of industrial wastes. This

research investigated the feasibility of SS as binder and aggregate in AAM, by determining the optimum

activation parameters and the pre-treatment process needed (wet-curing and carbonation). Mechanical,

microstructural and durability properties were evaluated via a series of characterization methods, such as

scanning electron microscopy (SEM), X-ray microtomography (μCT), mercury intrusion porosimetry (MIP)

and autoclave expansion, among others. Results showed that SS has low reactivity but may be alkaliactivated

as single binder. In fact, the best mechanical results (compressive strength up to 20 MPa) were

achieved by using an activator with low Na2O concentration (4%) and intermediary silica modulus (1.50-

2.22). As aggregate, the wet curing as pre-treatment of the SS is highly recommended for AAM and PC

matrices to control the delayed expansion of the former, producing sound materials after accelerated

testing. In addition, the ITZ showed a gel phase (most likely resulting from the reaction of the SS aggregate

in the alkaline system) which promoted the bond between aggregates and paste. On the other hand, the

carbonation as pre-treatment of SS strongly affected the strength development at early ages of AAM

mortars due to the formation of sodium carbonate in the activator. The AAM mortar designed with neat

SS as binder and aggregate presented low mechanical strength (up to 5 MPa) and high porosity.

Consequently, this mortar does not have sufficient mechanical strength to be evaluated in accelerated

expansion testing. The findings of this research showed that the use of SS as raw material is very

promising for AAM development.

COMMITTEE MEMBERS:
Presidente - PAULO HENRIQUE RIBEIRO BORGES
Interno - PETER LUDVIG
Externo à Instituição - ALI AGHAJANIAN SABBAGH
Externo à Instituição - CARLOS THOMAS GARCIA
Externo à Instituição - JOHAN BLOM
Externo à Instituição - JOÃO PAULO DE CASTRO GOMES