| To achieve scientific,rational and safe use of ground limestone,attain the purpose of energy saving and waste recycling,and consequently bring technical, economic and ecological benefits,the characteristics of cement-ground limestone gelation system is studied in detail in this dissertation.The study results can provide the theoretical and experimental basis for the technical system of production and application of ground limestone based cementitious material.The main contributions of this thesis are as follows:1.The hydration characteristic and relative rules of the ternary system of C3S-CaCO3-H2O and C3A-CaCO3-H2O are studied systematically.1) Microscopic tests of XRD,TG-DSC,IRS and calorimetry show that the addition of CaCO3 can change the hydration process of C3S without new hydration product and reduce induction period significantly.The first exothermic peak of the sample containing 25%CaCO3 appears in advance and is higher and narrower than that of the pure sample.The 24h exothermic quantity increases by 18.3%.Based on these,a hydration process model of C3S-CaCO3-H2O ternary system with acceleration characteristics of CaCO3 is proposed.2) XRD,TG-DSC and IRS analysis and SEM observation show that CaCO3 inhibits the generation of C3AH6 at early hydration period but promotes it along with the hydration process.CaCO3 inhibits the appearance of C4AH13 and C2AH8,and causes the formation of C3A·0.5CaCO3·0.5Ca(OH)2·11.5H2O and C3A·CaCO3·11H2O. The former appears in early hydration,totally being transferred after 1d hydration. The latter exists all the time during the initial hydration to 28d,and their appearance changes from thick flake in early hydration to long rod shape,being fine-needle when hydrated by 28d.The calorimetric analysis indicates that with the addition of CaCO3. the hydration heat of C3A has double-peak,which is different from that of pure C3A only.The hydration heat of C3A in 24h with the addition of 30%CaCO3 appears 2 times more than that of the pure C3A.2.The hydration characteristic of the quaternary system of C3A-CaSO4·2H2O-CaCO3-H2O are studied.XRD and DSC analysis prove that the hydration products of C3A-CaSO4·2H2O-CaCO3-H2O quaternary system are composed of C3AH6, C3A·CaCO3·11H2O,C3A·0.5CaCO3·0.5Ca(OH)2·11.5H2O,AFt and AFm.The formation time of C3AH6 is advanced by CaSO4·2H2O.Meanwhile,the hydration products'generation of C3A·0.5CaCO3·0.5Ca(OH)2·11.5H2O and C3A·CaCO3·11H2O is deferred,and the stability time of hydration product of C3A·0.5CaCO3·0.5Ca(OH)2·11.5H2O is elongated by CaSO4·2H2O.The stability of ettringite is also improved by CaCO3.The results of calorimetric analysis reveal that the hydration-induced heat-releasing characteristic of C3A under the co-action of CaCO3 and CaSO4·2H2O is plotted as three peaks.3.The hydration characteristic and pore structure of cement-ground limestone cementitious material system are studied.1) XRD,DSC and calorimetric analysis present almost a same law between the cementitious material system and single-mine.With the increase of ground limestone amount,C3A·CaCO3·11H2O advances its generation.Ground limestone defers the formation of ettringite and improves the stability of ettringite.The calorimetric analysis proves that the hydration process of cement is changed by the ground limestone.The addition of 10%ground limestone advances heat-releasing of cement hydration,increases heat-releasing speed and amount,shortens the induction period, advances the entering into the acceleration period ahead about 40 minutes and increases 8.5%heat of cement of per unit mass in 24h.2) The amount and fineness of ground limestone and water-binder ratio have effect on pore structure of harden paste by MIP analysis.The more the limestone is, the bigger the average diameter of harmful pore is,which means ground limestone increasing the probability of internal defect in cement paste.Using finer ground limestone and reducing water-binder ratio are beneficial to improve the pore structure of harden paste.4.The physical and mechanical property of cement-ground limestone cementitious material system are studied.1) With the increase of ground limestone amount,the fluidity of paste reduces while the fluidity of mortar and concrete increases,and the setting time is shortened. With the increases of ground limestone fineness,the fluidity of paste,mortar or concrete increases and the setting time is shortened.2) Ground limestone promotes the earlier hydration of cement and early strength of cement and concrete,but makes the later strength lower than normal concrete due to its pore coarsening effect.The strength of cement and concrete at 1d,3d and 7d increase firstly and then decrease along with the increasing of ground limestone.10% of ground limestone has the most obvious effect on improving early strength.When the amount of ground limestone is more than 20%,the addition of ground limestone does not improve the early strength(1～7d) of concrete.The strength of the sample containing ground limestone at 28d is lower than normal concrete,and the more of the limestone,the lower of the strength.5.The durability of cement-ground limestone cementitious material system are studied.1) Under the condition of sulfate or sulfate and chloride,the study on the durability of cement-ground limestone cementitious materials shows that the damages of the appearance including cracking,softening,abscission and ulceration.Under the action of single factor(sulfate),the hydration product of calcium carboaluminate can be decomposed after 6 months.The damage of specimens is mainly induced by the expansion of gypsum and the decomposition of hydration products of calcium carboaluminate.Under the action of two factors(sulfate+chloride),CaAl2 (CO3)2(OH)4·6H2O and transition product of calcium chloroaluminate are produced in the cementitious materials,accompanying with the appearance of much gypsum after 6 months.Both CaAl2(CO3)2(OH)4·6H2O and calcium chloroaluminate can be decomposed,producing easy-soluble CaCl2 after 20 months.Early damage of specimens is caused by volume expansion induced by gypsum crystallization,while further damage is mainly caused by gypsum,decomposition of CaAl2(CO3)2(OH)4·6H2O and calcium chloroaluminate,and the dissolution of CaCl2.2) The ground limestone accelerate the erosion damage of cement-based materials regardless of single factor or two factors,and the more of the ground limestone,the more of the deterioration.But under the two factors,chloride ions make no obvious difference in the generation of gypsum for the sample before and after being eroded,which relieves the erosion degree of the sample.
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