Evolution of Mechanical Properties with Time of Fly-Ash-Based Geopolymer Mortars under the Effect of Granulated Ground Blast Furnace Slag Addition

Abstract

Geopolymers are considered to alternatives to Portland cement, providing an opportunity to exploit aluminosilicate wastes or co-products with promising performances in the construction sector. This research is aimed at investigating the strength of fly-ash-geopolymers of different ages. The effect of granulated blast furnace slag (GGBFS) as a partial replacement of fly ash (FA) on the tensile (ft) and compressive strength (fc), as well as the modulus of elasticity, is investigated. The main advantage of the developed geopolymer mixes containing GGBFS is their ability to set and harden at room temperature with no need for heating to obtain binding properties, reducing the energy consumption of their production processes. This procedure presents a huge advantage over binders requiring heat curing, constituting a significant energy savings and reduction of CO2 emissions. It is found that the development of strength strongly depends on the ratio of fly-ash to granulated blast furnace slag. With the highest amount of GGBFS, the compressive strength of geopolymers made of fly-ash reached 63 MPa after 28 days of curing at ambient temperature. The evolution of compressive strength with time is correlated with the development of ultrasound pulse velocity methods, which are used to evaluate maturity. The modulus of elasticity changes with strength and the relationship obtained for the geopolymer is presented on the basis of typical models used for cement-based materials. The tensile to compressive strength ratios of the tested geopolymers are identified as higher than for cementitious binders, and the ft(fc) relationship is juxtaposed with dependencies known for cement binders, showing that the square root function gives the best fit to the results.

Analysis of Changes in the Microstructure of Geopolymer Mortar after Exposure to High Temperatures

“…This products locate in pores in the microstructure. The effect of the decrease in porosity was seen for the sample without GGBFS addition with lower strength at room temperature [ 20 ]. According to the literature [ 40 ], geopolymers with lower strength at ambient temperature may retain more unreacted particles of raw materials, which, after creating appropriate hydrothermal conditions, can be transformed into geopolymerization reaction products.…”

“…Test results [ 19 ] indicate that the addition of slag in the amount of only 4% improves the strength of the material. Using a mixed FA-GGBFS binder in the 1:1 ratio, it is possible to obtain a mortar with compressive strength above 60 MPa after 28 days of curing without additional temperature treatment at the material setting stage [ 20 ]. The partial replacement of fly ash by ground granulated blast-furnace slag strengthens the structure of the material and can also accelerate the curing of the geopolymer at room temperature.…”

Fly-Ash-Based Geopolymers Reinforced by Melamine Fibers

“…Almost three decades ago, the French scientist Joseph Davidovits introduced the term “geopolymers” for aluminosilicate polymers formed in an alkaline environment [ 1 , 2 , 3 ]. Most geopolymer synthesis methods come down to one process, in which comminuted dried pozzolanic material (such as metakaolin [ 4 , 5 , 6 ], fly ash [ 7 , 8 , 9 , 10 ] or blast furnace slag [ 11 , 12 ]) is mixed with an aqueous solution of a suitable silicate (e.g., sodium or potassium silicate) with the addition of a strong base, usually concentrated sodium or potassium hydroxide. The resulting paste behaves similarly to the cement paste.…”

The immobilisation of heavy metals from sewage sludge ash in geopolymer mortars

“…5.0 MPa and the compressive strength was nearly 45.5 MPa. The results are around 30% lower than those of the FA-GGBFS mixed binder [31]. Mixtures containing only SSA binders or SSA in combination with FA binders had a significantly lower strength.…”