Study On Preparation And Properties Of Geopolymer-based Pavement Brick

Geopolymers prepared from industrial solid wastes such as slag and fly ash can emit no harmful gases and can replace cement as a cementing material,which is of great significance for environmental protection and resource recycling.Therefore,it is proposed to use slag as the main raw material to prepare geopolymer-based pavement bricks by an alkali activating method.The effects of the type and amount of alkali activator,water glass modulus,water-cement ratio,curing temperature,and fly ash content on the strength of slag-based geopolymer materials and their resistance to sulfate attack were studied.The material structure and morphology were investigated by the means of XRD,SEM,EDS,and the appropriate conditions and optimal mix ratio for the preparation of geopolymers were determined.The compressive strength,water absorption,abrasion resistance,and frost resistance of the brick were studied.The micromorphology of products was analyzed.the result shows:Factors such as the type and amount of activator,water glass modulus,and water-cement ratio have a great impact on the compressive strength of the material.The strength of material with water glass as an activator is significantly higher than that of materials with NaOH,Na₂CO₃,and Na₂SO₄.The suitable conditions for preparing slag-based geopolymers are 1.2 of water glass modulus,10 wt%of dosage,0.32 of the ratio of water to cement and 70 °C of curing temperature.XRD,SEM,and EDS tests show that the main hydration products of the slag base geopolymer are hydrated calcium silicate and ettringite.The introduction of fly ash significantly improved the compressive strength of the geopolymer material in the slag base.As the amount of fly ash increases,the strength of the material increases first and decreases then.When its content is 20%,the strength of the sample reaches the maximum,which is 45.7 MPa.The main hydration products of slag-fly ash based geopolymer materials are hydrated calcium silicate,water garnet,anorthite and so on.The slag-based and slag-fly ash-based geopolymers have significantly better resistance to sulfate attack than ordinary portland cement.SEM and EDS tests and analysis show that after sulfate attack,the hydration products of the slag based geopolymer are mostly reticulated calcium aluminosilicate?C-A-S-H?;the hydration products of the slag-fly ash base geopolymer are mainly alkali aluminosilicate gel?N-A-S-H?and C-A-S-H;the ordinary portland cement erosion samples cracked because of volume expansion due to the formation of acicular hydrated calcium sulfoaluminate?AFt?.The water absorption,abrasion resistance and frost resistance of geopolymer-based pavement samples prepared with water glass as an activator are significantly better than those prepared by NaOH.The 28 day compressive strength reaches 49.2 MPa,which meets the requirements of C40 pavement bricks.The water absorption and abrasion resistance of slag geopolymer-based pavement bricks are 1.1% and 3.7% respectively;The water absorption and abrasion resistance of slag-fly ash geopolymer-based pavement bricks are 1.0% and 3.8%;after 50 freeze-thaw cycles,the compressive strength loss rates of the two pavement bricks and mass loss rates are 6.32% and 0.41%,4.13%,and0.82%;the morphology of the hydration product is relatively complete,which are the reasons that the slag geopolymer-based pavement bricks show good resistance to frost.Figure 48,Table 25,Reference 57...