Advances in Civil Engineering

Review Article

Thermal and Mechanical Properties of Geopolymers Exposed to High Temperature: A Literature Review

Table 4

Strength characteristics of MK geopolymers at high temperature.
ResearchersTchakoute et al. [76]Lahoti et al. [77]Aygörmez et al. [78]Duan et al. [43]Duan et al. [79]Rovnaník and Šafránková [53]Duan et al. [60]Zhang et al. [80]Roviello et al. [81]Yan et al. [82]Villaquirán-Caicedoa et al. [83]Kovářík et al. [52]Burciaga-Díaz and Escalante-García [84]
AdditiveSodium waterglass (NWG)Silica fume (SF)SF and colemanite waste (CW)FAFAFAPolystyrene particles (PP)FABasalt microfibril (BMF)Carbon fiber (CF) and SiC fiber (SCF)Aluminosilicate particles (AP), CF, and alumina fibers (AF)Ceramic particle (CP)BFS
VariablesThe addition of NWG from RHA and waste glass (WG)Si/Al molar ratio in 1.03–2.00The addition of SF, CW, and polypropylene fiber (PF)The addition of OPC and FAThe addition of OPC and FAFA and MK geopolymersThe addition of PPThe addition of FAThe addition of BMFDifferent temperatures and fiber lengthsThe addition of reinforcing materialsThe addition of CPThe addition of BFS
The result of strengthThe strength decreases from room temperature to 400°C and then increases until up to 800°C.Geopolymers with Si/Al ratio of 1.75 possess highest strength (6 MPa) after exposure to 900°C.The inclusion of SF up to 20% and CW up to 10% increased the residual compressive and flexural strengths, while PF yields slight decrease.The strength of OPC paste is almost zero at 600°C, while that of FA/MK geopolymer decreases to 46 MPa at 1000°C.The compressive strength of OPC paste decreases significantly after 400°C, while that of geopolymers increases after 400°C.MK geopolymer shows better mechanical properties compared to FA geopolymer under laboratory conditions. But high temperature turns the results into opposite.The strength of geopolymers decreases with the increase of PP content, but still shows sufficient strength.Blended MK/FA geopolymers show higher bending and compressive strength both at ambient temperature and after exposure to 800°C.The incorporation of BMF increases the strength due to its increased thermal resistance and dense microstructure. The composite of 10 wt% BMF possesses the best residual strength.The room temperature mechanical properties are improved remarkably due to the inclusion of hybrid fibers. The SCF with the length of 3 mm exhibits the highest retention of strength.The reinforcement composites of AF/AP and CF/AP achieve remarkable mechanical performance both at room and high temperature.The geopolymers incorporating fine CP (under 90 mm) at the amount of 250% of MK weight have a constant flexural strength of ∼12 MPa and a compressive strength of ∼90 MPa, both before and after exposure at 1000°C.The binders of 50%BFS-50%MK and 100% BFS retain the strength better than 100%MK at the range of 600–800°C. But the trend changes when the temperature is over 1000°C.
Residual strengthIt is about 103% and 117% at 600°C and 92% and 98% at 800°C for NWG-RHA and NWG-WG geopolymers, respectively.It is about 0, 11%, 3%, 9%, and 4% at 900°C for the Si/Al ratio of 1.03, 1.25, 1.5, 1.75, and 2.00.It is about 48.1% (10% SF) and 47.3% (10% CW) at 600°C and 17.1% (10% SF) and 15.8% (10% CW) at 800°C.It is about 100%, 81%, and 78% at 600°C, 800°C, and 1000°C, respectively, for the geopolymer pastes.It is about 97%, 84%, and 72% at 600°C, 800°C, and 1000°C, respectively, for the geopolymer pastes after 3 days of curing.It is about 72%, 72%, and 64% at 600°C, 800°C, and 1000°C, respectively, for MK pastes and 217%, 410%, and 422% for FA paste.It is about 32%, 29%, 28%, 25%, and 17% at 800°C for the 0, 25%, 50%, 75%, and 100% addition of PP, respectively.The retention ratio in bending and compressive strength is 4% and 44%, respectively, after exposure to 500°C.It is about 68% and 57% at 400°C and 800°C, respectively, for the incorporation of 10 wt% BMF.It is about 108%, 72%, and 77% at 800°C, 1000°C, and 1200°C, respectively, for the SCF length of 3 mm.It is about 265% and 227% after exposure to 1200°C for reinforcements of CF/AP and AF/AP, respectively.It is about 100% and 98% for the flexural and compressive strengths at 1000°C.It is about 58%, 55%, and 30% at the temperature of 800°C, 1000°C, and 1200°C, respectively, for the binder of BFS : MK = 1 : 1.