English abstract
Concrete/mortar is the most used building material in the world. Its production requires
the use of clinker cement as a binding material, whose manufacturing consumes a large
amount of energy leading to the emission of around 8 to 10% of the global carbon dioxide
(CO2) released to the atmosphere. Therefore, clinker cement is considered as a significant
environmental pollutant and a non-environmentally friendly material. In the last recent
decades, extensive research works have been done and are still ongoing in the field of
materials and environmental integration. These efforts tend to modify or propose some
viable alternative materials to Ordinary Portland Cement. Cementitious/pozzolanic
materials (SCMs) derived from natural or industrial resources have been incorporated into
concrete/mortar to minimize the environmental charges of cement manufacturing. SCMs
and alternative additives in concrete may enhance not only the sustainability of concrete
in multiple ways but also its mechanical and durability performances.
In this study, raw clay soil was collected from a selected region in Oman called Fanja
(FNJ). The clay was ground to a fineness of less than 75 µm and then subjected to a series
of chemical, physical, and thermal characterization to assess its pozzolanic or cementing
potential as a cement replacement material in mortar. The chemical analysis showed that
the sum of (SiO2 + Al2O3 + Fe2O3) of FNJ clay is higher than 93%, which qualifies it as a
pozzolanic material. Thermogravimetric and differential thermal analysis were used to
select four different most suitable and optimum calcination temperatures (700, 800, 850,
and 950 °C). The burnt ground clay was then used as a partial replacement pozzolana of
Portland cement in mortar production designed with a constant water-to-cement (w/c)
ratio of 0.30.
The efficiency of using this calcined FNJ clay as pozzolana in mortar was assessed in two
phases. The first phase involves using the four calcined clay in the mortar mixtures as a
binary system with different replacement percentages (5, 10, 15, 20, 25, and 30%). The
second phase involves using the optimum calcination temperature, and replacement
percentage of FNJ based on the crystal structure change and strength results of the binary
mortar mixes investigated in the first phase. The optimum mix (10%FNJ850) with a
calcination temperature of 850 °C and percentage replacement of 10% was combined with
various SCMs.
Binary and composite cement mortar mixes were assessed at their fresh and hardened
states. The compressive strength test was conducted at different ages (1, 7, 28, and
91) days. After 28 days of wet curing, flexural strength, thermal conductivity, Ultrasonic
pulse velocity (UPV), and resistance to elevated temperature were examined. Moreover,
the durability performance was assessed in terms of porosity and water absorption, and
chloride permeability. Resistance to chemicals was evaluated by submerging mortar
samples in a 5% concentration of (sodium sulfate + sodium chloride) solution, as well as
acidic solutions, including sulfuric, hydrochloric, and nitric acids.
The main findings indicate that using FNJ has delayed the final setting time and increased
the normal consistency. The inclusion of FNJ pozzolan reduced the mortar`s flow, which
requires a slight increase in the superplasticizer demand as the replacement level of FNJ
increases. The fresh and hardened densities of mortars made with FNJ Pozzolana
remained mostly the same. However, for both binary and composite cement mortars, the
1-day compressive strength decreased up to -68%, while the longer-term strength
measured at 7, 28, and 91 days enhanced by around 111%, 86%, and 66%, respectively.
While a slight reduction in the porosity and absorption was recorded when adding FNJ
pozzolana to the mortar mix, a negligible effect on the UPV and thermal conductivity
values was found. Meanwhile, a tremendous reduction in the chloride permeability was
reached as the FNJ content increased. In addition, blended FNJ mortar has improved the
mortar's resistance against sulphate and acids attacks compared to the control mortar.
Finally, using a combination of local calcined clay as a pozzolanic material to partially
substitute Portland cement in mortar mixes resulted in a more economical with higher
strength, better durability, long-lasting, and more environmentally friendly material.
Keywords: acids resistance, calcined clay, cementitious and pozzolanic material,
fineness, strength, durability, porosity, sulphate resistance, thermal conductivity.
