Study On The Cementitious Materials With Low Alkalinity For Environmentally Friendly Concrete

This research programe is a part of the Ministry of Water Resources' 948 Plan, namely technical innovation and transformation projects, study on techniques of steep rock slope eco-engineering. The dissertation presents laboratory test that hardened cementitious paste has not only moderate strength to protect steep slope, but also low pH value suitable for plant growth.Theoretical analysis on three series of cements, i. e. Portland cement, high alumina cement and sulpho-aluminous cement, shows that alkalinity of the pore fluid of the balanced hydration product of sulpho-aluminous cement is the lowest, and its strength and alkalinity can be adjusted further by the adjustment of its components.With integration of the requirements of strength of hardened cement paste and alkalinity of its pore fluid, two formulas, H30-1 and H50-6, are primarily selected for biobed materials. Experimentations of the effect of alkalinity of the pore fluid of hardened paste on soil alkalinity and compressive strength of the porous concrete show that the pH value of H50-6 Formula decreases by 20% with comparison to that of Portland cement, alkalinity of soil pore fluid is only increased by 7% at 5 hours, and is stabilized at 7 days. At the same time, it reflects the designed test method and layered soil sampler are effective to the analysis of alkalinity of soil pore fluid. At 90 days, cubic compressive strength of the porous concrete of H50-6 Formula reaches 10.4 MPa with filling rate of 40% and artificial aggregates, while that of H30-1 Formula decreases. Test results of plantadaptability shows that cementitious materials of H50-6 Formula is suitable for biobed by the normal growth of green stonecrop.SEM micro-tests reveals that the antecedent strength of hardened paste of H50-6 Formula originates from ettringite, a hydration product. Later on, hydration of fly ash, slag and gypsum produces gel material enwrapping the surface of ettringite, which increases the strength of H50-6's hardened paste on the one hand, and hold back ettringite weathering on the other hand. So ettringite decomposition is effectively controlled so as to avoid strength decrease of the hardened paste.