Interaction Between Hydration Products And Clay Minerals And Constituent Design Methodology Of IBPs-based Cementitious Materials In Stabilized Clay

Cement is a commonly used cementitious material in soft clay stabilization.Depending upon the source of clay being formed,the strengths of cement-based stabilized clay（CBSC）show a distinct variability as compared to concrete and mortar,the reason can be attributed to the interaction between clay minerals and hydration products.However,the related mechanism has not yet been well recognized presently,thus limits the development of cementitious materials significantly.To better understand the interaction between clay minerals and hydration products as well as the strength generation of CBSC,a series of laboratory and field tests were systematically investigated by referring the newly advanced and cross disciplinary testing analyzing frameworks.The main conclusions are summarized as follows:（1）A new quantitative framework that distinguishes the two major contributors,cementation and density,was proposed.Additives such as silica fume and foaming agent,were used to finely tune the cementation bonding strength and porosity respectively so that the effects of density and cementation on strength development can be separately identified and quantified.Results indicated that the strength is more sensitive to density in CBSC,suggesting the importantance of density control in CBSC.（2）Adjusting gypsum fraction in the OPC’s constituents was proposed as a cost-effective and environmentally friendly technology for the improvement of soft clays with high initial water contents as well as the beneficial reuse of industrial gypsum waste.The mechanical performance of CBSC treated with different G/C ratios was investigated using a series of laboratory tests,including final water content,final dry densitiy,strength and modulus.Results reveal that the gypsum fraction has a significant influence on the index and mechanical properties of CBSC,and there exists a threshold of G/C ratio that governed by the initial water content.Microstructure characterization shows that the newly formed ettringite acts as significant pore infills,and the associated remarkable volumetric expansion is responsible,and may be the primary factor,for the beneficial strength gain due to the added gypsum.（3）Two commercially available clays（i.e.,kaolin and bentonite,whose dominant clay minerals are kaolinite and montmorillonite,respectively）stabilized by two key functional constituents of cement clinker,i.e.,tricalcium silicate（C₃S）and tricalcium aluminate（C₃A）,were investigated to understand the cement-clay reactions.Strength sensitive factor was proposed as a parameter to characterize the selectivity of clay minerals to clinker consitituents.Results shown that kaolinite clays are more sensitive to C₃S,while montmorillonite clays are more sensitive to C₃A.（4）The micro-nano interaction between clay minerals and hydration products were revealed by atomic force probe microscopy（AFM）,grid nanoindentation（NID）,²⁹Si/²⁷Al nuclear magnetic resonance（NMR）,fourier transform infrared spectroscopy（FT-IR）,thermogravimetric analysis（TGA）,and mercury intrusion porosimetry（MIP）tests.Deconvolution statistical analytics of the obtained large data sets were carried out through probability density function（PDF）and cumulative distribution function（CDF）.The phase generation,distribution and transformation behaviors during the interaction between hydration products and clay minerals are comprehended.（5）During the secondary pozzolanic reaction process,the dissolved colloids from the clay minerals and the hydrated products would react and accumulate at the interface between the primary cementitious paste and clay particles to form a new soft porous phase.The deconvolution and thermogravimetric analysis indicate that more pozzolanic products and high-density（HD）porous phases were detected in stabilized bentonite than in kaolin counterpart,suggesting that the pozzolanic reaction in montmorillonite is much more pronounced than that in kaolinite.（6）A newly generic framework by unifying different industrial by-products（IBPs）as composite binders to potentially replace OPC for soft clay stabilization was proposed.The concepts of three chemical moduli（TCM）and strength activity index（SAI）were used to determine the fractions of different IBPs,and the design mix is further tuned by adding gypsum for additional strength gain contributed by density due to ettringite formation.Thereafter,stabilized Fuzhou soft clay（via laboratory test）and Foshan mud（via in situ deep cement mixing method）were selected as two case studies to explore the feasibility of the proposed framework when encountering soils with different clay mineralogy.Results indicated that the integrity and mechanical properties of the stabilized samples using the proposed framework were better than those of the OPC counterparts.