Permeability modeling of self-healing due to calcium carbonate precipitation in cement-based materials with mineral additives

The permeability modeling of self-healing due to calcium carbonate precipitation in cement-based materials with mineral additives was studied in this work. The parameters of calcium carbonate precipitation during self-healing were simulated. A permeability modeling of self-healing, combined with numerical simulation of calcium carbonate formation, was proposed based on the modified Poiseuille flow model. Moreover, the percentage of calcium carbonate in healing products was measured by TG-DTA. The simulated results show that self-healing can be dramatically promoted with the increase of pH and Ca2+ concentration. The calculated result of permeability is consistent with that measured for cracks appearing in middle or later stages of self-healing, it indicates that this model can be used to predict the self-healing rate to some extent. In addition, TG-DTA results show that the percentage of calcium carbonate in healing products is higher for mortar with only chemical expansion additives or cracks appearing in the later stage, which can more accurately predict the self-healing rate for the model.

Effect of mineral additives and permeability reducing admixtures having different action mechanisms on mechanical and durability performance of cementitious systems

In this paper,the effect of usage of the permeability reducing admixture(PRA)having different action mechanisms on hardened state properties of cementitious systems containing mineral additives is examined.For this aim,three commercial PRAs were used during investigation.The effective parameters in the first and third PRAs were air-entraining and high-rate air-entraining,respectively.The second one contained the insoluble calcium carbonate residue and had a small amount of the air-entraining property.Mortar mixes with binary and ternary cementitious systems were prepared by partially replacing cement with fly ash and metakaolin.The hardened state properties of mortar mixtures such as compressive strength,ultrasonic pulse velocity,water absorption,drying shrinkage and freeze-thaw resistance were investigated.The ternary cement-based mixture having both fly ash and metakaolin was selected as the most successful mineral-additive bearing mix in regard to hardened state properties.In this sense,PRA-B,with both insoluble residues and a small amount of air-entraining properties,showed the best performance among the mixtures containing PRA.The combined use of mineral additive and PRA had a more positive effect on the properties of the mixes.

Effect of Alternative Raw Materials on Resistance of Concrete to Chemical Actions

The results of experimental works aimed on finding the optimal composition of concretes containing alternative materials as mineral additives for assurance their high resistance to chemical aggressive attack are presented in the paper. 4 kinds of additives （blast furnace slag, fly ash, non-treated and treated serpentinite waste） and 4 kinds of aggressive environments （distilled water, HCI, MgSO4 and NaOH） representing the concrete corrosive processes was checked within experimental process. The open laboratory curing was used as a reference environment. Moreover, the amounts of additives were varied, so 16 various recipes were checked on the whole. The resistance of samples was tested in the terms of flexural strength, compressive strength and evaluation of decrease/increase of strengths after long time （28 months） exposition in monitored aggressive media. Based on obtained results, it is possible for each of aggressive environments recommend the most promising recipe from various points of view, in accordance with user＇s priorities. From the percentage increase of 28-day compressive strengths point of view, there are： for HCI action - recipe with 20% of non treated serpentinite waste with plasticizer application, for MgSO4 action - recipe with 20% of blast furnace slag without plasticizer application and for NaOH action - recipe with 10% of non treated serpentinite waste without plasticizer application. Application of alternative materials as partial substitution of cement appears to be beneficial for achievement the resistance to aggressive chemical actions. With the keeping or enhancement of technical parameters it extra represents both the environmental and economic benefit.

Evaluation of Porous Structure of Cement Pastes Made with Residual Rice Husk Ash

In several countries, the residual RHA （rice husk ash） has been produced in rice processing industries or in thermoelectric plants that use rice husk to generate heat and/or electrical energy, usually without burning process control. This causes a reduction in the amorphous silica content of residual RHA, which distinguishes them from the RHA produced according to controlled burning process, which is totally amorphous and considered a highly reactive pozzolan. In this paper, the hydration products and the porous structure of binders paste were studied by replacing, in weight of 5%, 10% and 20% of Portland cement OPC （ordinary Portland cement）, by residual RHAs named A and B, which have high and low content of amorphous silica, respectively, using microstructure evaluation techniques as XRD （X-ray diffraction）, TG （thermogravimetric） tests and MIP （mercury intrusion porosimetry）. A reducing the size of the pores of the pastes was observed according to the increase of content replacement of RHA A and RHA B.

Mechanical behavior and permeability properties of sustainable and high-performance anisotropic three-dimensional printable concrete

Three-dimensional printable concrete requires further development owing to the challenges encountered,including its brittle behavior,high cement requirement for the buildability of layers,and anisotropic behavior in different directions.The aim of this study is to overcome these challenges.First,three-dimensional printable concrete mixtures were prepared using silica fume,ground blast furnace slag,and metakaolin,instead of cement,to reduce the amount of cement.Subsequently,the rheological and mechanical behaviors of these concretes were investigated.Second,threedimensional printable concrete mixtures were prepared using 6-mm-long steel and synthetic fibers to eliminate brittleness and determine the effect of those fibers on the anisotropic behavior of the concrete.As a result of this study,it is understood that printable concretes with extremely low permeability and high buildability can be achieved using mineral additives.In addition,results showed that three-dimensional concrete samples containing short steel fibers achieve fracture energies up to 36 times greater than that of plain concrete.Meanwhile,its characteristic length values,as indicators of ductility,are 22 times higher than those of plain concrete.The weakest strength was recorded at the interfaces between layers.The bending and splitting tensile strengths of three-dimensional printed plain concrete samples were 15%and 19%lower than those of casted samples,respectively.However,the addition of fibers improved the mechanical strength of the interfaces significantly.