Research On The Development And Biological Corrosion Resistance Of Cement-based Materials Mixed With Aluminum Sludge

In recent years,as a waste of drinking water treatment,the output of drinking water treatment sludge（DWTS）increased greatly,and the inadequate disposal made it have potential to harm the human health and the ecological environment.Therefore,how to utilize DWTS economically and environmentally has become the focus.Drinking water sludge ash（DWSA）is rich in aluminum and has a similar composition to aluminate cement with anti-corrosion properties.Calcination can stimulate the pozzolanic activity of DWSA and then it can be used as a pozzolan to improve the corrosion resistance of cement-based materials in sewage environment.In this paper,a total of four kinds of DWTS were selected in Xi’an and South Australia,and the basic characteristics of DWTS were comparative characterization.DWTS taken from South Australia is dried,ground,and calcined to prepare DWSA;the optimal calcining temperature of DWTS is studied,and DWSA is used as a supplementary cement material to prepare cement-based materials;the influence of DWSA on the macroscopic properties and hydration process of cement-based materials is discussed,and pay attention to its impact on the resistance of cement-based materials to biological sulfuric acid attack.The results are as followed:（1）The main components of DWSA are Al and Si.And the surface of DWSA is rough and porous,with a loose structure and large specific surface area.Experiments have shown that 800 ^oC is the best pretreatment temperature for DWTS.At this calcination temperature,crystalline substances such as kaolinite and aluminum in DWTS will transform into amorphous and semi-crystalline states to obtain active DWSA with high content of aluminum.（2）DWSA significantly increased the water demand of the blended paste;increased the capillary water absorption of the test mortar;reduced the fluidity of the mortar;changed the setting time of blended paste,but finally,it was confirmed the requirement of standard GB175.The test mortar with 30%content of DWSA has the highest strength at 90 days.（3）During the hydration process,DWSA will affect the cement hydration process through three aspects:filling effect,dilution effect,and pozzolanic activity.The pozzolanic reaction mainly occurs after 7 days.The addition of DWSA promotes the formation of aluminum-containing phase hydrates such as C-A-H and C-S-A-H,and consumes the CH generated by cement hydration.The low content of DWSA makes the matrix structure denser,and the total porosity is increased with the high content of DWSA.Combining the macro performance and micro characterization,considering the durability of the test piece,it is recommended that the optimum content of DWSA should be 10%.（4）The A.f bacteria liquid cultured for 1-2 d was used as the corrosive medium to carry out the biological sulfuric acid corrosion test.The results showed that during the corrosion process,the hydration products of the cement-based material gradually dissolved and formed corrosion products such as gypsum and ettringite.A large number of jarosite crystals are generated outside the corrosion layer,which provides additional compressive strength for the mortar so that the strength of mortar after corrosion increased.Besides,a large number of A.f colonies are observed on the surface of the samples.（5）Evaluation indicators such as quality loss,corrosion depth,and Ca²⁺dissolution concentration showed that the optimal dosage of DWSA is 10%under biological sulfuric acid corrosion conditions.The addition of 10%DWSA promotes the hydration of cement and the formation of aluminum-containing hydrates,which make cement-based materials more acid-resistant.When the content of DWSA increased,the porosity of DWSA accelerates the mass transfer process of the corrosive medium,which reduces the durability of cement-based materials.