Selected Research Activities for A. Zayed (funded by FDOT/FHWA/NSF)
Areas of Research: Construction materials characterization (microstructure, chemical, physical and mineralogical), concrete and steel properties assessment and relationship between microstructural, morphological and mineralogical evolution (phase transformation), mechanical properties evolution and concrete performance/durability (cracking potential, shrinkage, adiabatic temperature rise, and unsoundness).
Types of Materials: Construction materials including steel, concrete, cements, aggregates, supplementary cementitious materials (SCMs) such as slag, silica fume, coal ashes, metakaolin, low-grade kaolinitic calcined clay and chemical admixtures.
Selected research projects synopsis:
1. Characterization (microscopic) of the steel-concrete interface in plain concrete and concrete blended with supplementary cementitious materials (silica fume).
a. The concrete system is comprised of cement paste and aggregates (fine and coarse). The interface between aggregates and cement paste or reinforcement is referred to in the literature as “interfacial transition zone (ITZ)”. ITZ is the weakest link in concrete and enhancing its properties improves concrete strength. The study addressed quantifying porosity and phases/compounds abundance in the concrete microstructure and the role of supplementary cementitious materials in concrete mixtures on the physical and mineralogical characteristics of ITZ.
2. Studies on coal burning by-products (Class C and Class F fly ashes) and their effect on concrete durability and performance.
a. In addition to the typical constituents of concrete (cement, water, fine and coarse aggregates) concrete contains SCMs as well as chemical admixtures. Admixtures affect concrete fresh and hardened properties such as setting time, temperature rise, strength gain, as well as durability (chlorides, sulfates, shrinkage, cracking potential, adiabatic temperature rise, etc..). The effectiveness of fly ash quality (Class F and C) on concrete durability was the focus of several studies.
3. Studies on the effects of portland cement characteristics on concrete durability.
a. Several sources of the same type of portland cement were studied to assess their characteristics and the effect of cement characteristics on strength and durability of concrete. The findings indicate source variability of the same type of portland cement results in differences in the phases assemblage (mineralogy) of the hydration products and subsequent durability performance and strength development.
4. High-early-strength concrete and the role of different chemical admixtures (accelerators) dosages on its durability.
a. This study focused on the effect of controlling constituents of portland cement concrete to minimize concrete cracking potential while satisfying open-to-traffic criterion of 6 hours for concrete mixtures used in slabs replacement.
5. Alternatives for traditional supplementary cementitious materials used in concrete mixtures (low-grade kaolinitic calcined clay).
a. The focus of studies conducted in this area was to find an alternative to the currently used supplementary cementitious materials (SCM) due to anticipated supplies shortage. SCMs are used to partially replace portland cement in concrete mixtures. When used in appropriate dosage and appropriate quality, they enhance concrete durability and performance. The studies addressed a widely available material, kaolinitic clay, for its potential use as an SCM in structural elements. To this end, several clays from different locations in the southeast (Georgia and Florida) were acquired, characterized and assessed for their performance in concrete in lab studies. The next step in this research is to have an implementation project where the material can be used in different structural elements.
6. Adiabatic temperature rise, durability and performance of slag blended concrete.
a. The study was initiated when field reports indicated instances where large structures experienced temperature rise close to/above 185°F. The concrete mixtures all contained ground granulated blast furnace slag (GGBFS, slag). The role of slag materials characteristics was first studied, followed by examining slag performance as SCM in concrete mixtures. The effect of slag content on concrete performance was also assessed. Several durability issues were addressed and related to the slags as-received materials characteristics. Adiabatic temperature rise, performance in marine conditions (sulfates and chlorides exposure), cracking potential and shrinkage are some of the testing conducted in assessing performance. The findings of this study included providing FDOT with specifications recommendations pertaining to slag materials characteristics for use in concrete, adopted in “FDOT Standard Specifications for Road and Bridge Construction FY 2023-2024 Section 929-4”.
Links for selected Final Reports that can be accessed from FDOT website:
https://fdotwww.blob.core.windows.net/sitefinity/docs/default-source/research/reports/fdot-bdv25-977-28-rpt.pdf
https://fdotwww.blob.core.windows.net/sitefinity/docs/default-source/research/reports/fdot-bdv25-977-63-rpt.pdf?sfvrsn=f55aff5e_2
