Experimental Study On The Mechanical Properties Of One-part Geopolymer Concrete And Its Beam

Geopolymer,as an environmentally friendly material and a potential substitute for cement,has been reported to possess comparable mechanical properties with cement.The production of geopolymer generally uses alkaline solution reacting with silicon-alumina precursor materials but the inconvenience of alkaline solution in storage and transportation limits the large-scale engineering application of geopolymer.If a solid activator can be used instead of activator solution,the solid alkaline activator powders are mixed with precursor material in advance,and just adding water to produce one-part geopolymer will greatly improve the convenience of geopolymer concrete construction.At present,there are few investigates on the comparison of the mechanical properties and reaction mechanism between one-part and two-part geopolymer,and the research on the mechanical properties of one-part geopolymer concrete components is even rarer.In present study,a lot of experiments had been conducted and the optimal mix of one-part geopolymer concrete was obtained.The differences in reaction mechanism and mechanical properties between one-part and two-part geopolymer were revealed,and the flexural design method of one-part geopolymer concrete beam was proposed,which provide an experimental data support and a theoretical basis for engineering applications.The main research work and conclusions of present study are as follows.1.Flexural and compressive tests were carried out on 7 groups of one-part geopolymer mortars and 5 groups of two-part geopolymer mortars with a size of 40×40×160mm,and the tests of reaction heat within 7 days and degree of reaction at 7^th day were conducted.The effects of types,concentration and modulus of activators on workability and mechanical properties of one-part and two-part geopolymer mortars were evaluated,the reaction mechanism of one-part geopolymer was found out.The results show that:（1）All of the flexural and compressive strengths of one-part geopolymer mortar were lower than that of corresponding two-part geopolymer mortar,and the flexural strength ratio and compressive strength ratio of the former to the latter is 88%～94%and 65%～95%respectively,while the fluidity of one-part geopolymer mortar were better than two-part geopolymer mortar.（2）The early strength of one-part geopolymer was relatively high and the strength development after 7 days was limited.（3）Anhydrous sodium silicate（Na₂Si O₃）was a more effective solid activator than the combination of hydrous Na₂Si O₃ and Na OH for one-part geopolymer mortar,due to a higher degree of reaction and greater reaction heat under same concentration and modulus of activators.（4）When using the combination of hydrous Na₂Si O₃ and Na OH as activator,the improving effect of decreasing the modulus of activator on the strength in one-part geopolymer mortar is less effective than that in two-part geopolymer mortar.2.Fifty-four cubic specimens with a size of 150×150×150 mm and fifty-four cylindrical specimens with a size ofФ150×300 mm were tested under uniaxial compression.The effects of proportion of slag,alkali content and water to binder ration on the compressive strength,elastic modulus and shape effect of one-part geopolymer concrete were evaluated.Besides,the optimal alkali content and the production cost of one-part geopolymer concrete with different slag proportions were analyzed,and the optimal geopolymer concrete mix was obtained.The results show that:（1）Partially replacing metakaolin with slag could reduce the alkali dosage of geopolymer,but the mechanical properties of geopolymer were not significantly reduced.（2）In the precursor mixture of fly ash,metakaolin and slag,the optimal alkali content of one-part geopolymer concrete with 10%,20%and 30%slag proportions were 11%,8%and 7%respectively.In general,the optimal alkali content decreased with a decrease in Si/Ca.（3）With an increase of water to binder ratio,the difference in compressive strength between one-part and two-part geopolymer concretes decreased,while that in elastic modulus has no variation.（4）The shape effect on the compressive strength of one-part geopolymer concrete was not significant.（5）The elastic modulus of one-part geopolymer concrete could reach more than 75%of elastic modulus of cement concrete predicted by ACI code.3.Five reinforced concrete beams were tested under flexural loading.The flexural performance of one-part geopolymer concrete beam with different tensile reinforcement ratios was evaluated,and compared with the corresponding two-part geopolymer concrete and ordinary cement concrete reinforcement beams.The results indicated that:（1）The cracking pattern and failure mode of reinforced one-part geopolymer concrete beam were similar to that of reinforced ordinary concrete beam,and the cracking load and ultimate load of both were comparable.However,the ductility of the former was slightly lower and the deflection was higher under equal loading.（2）The crack resistance of reinforced one-part and two-part geopolymer concrete beam were almost equivalent,however,the extension height of vertical crack in the former was significantly higher than that of the latter,and the ductility of reinforced one-part geopolymer concrete beam was better.（3）The cracking load and ultimate load of reinforced one-part geopolymer beams were agree well with the predicted value calculated by the formula applied to reinforced ordinary concrete beam.（4）The minimum reinforcement ratio of one-part geopolymer concrete beam was higher than that of ordinary concrete beam,and the maximum reinforcement ratio of the former was lower than that of the latter.The range of reinforcement ratio of under reinforced one-part geopolymer concrete beam was narrow than that of ordinary concrete beam.