Multi-scale simulation of capillary pores and gel pores in Portland cement paste

The microstructures of Portland cement paste (water to cement ratio is 0.4, curing time is from 1 day to 28 days) are simulated based on the numerical cement hydration model, HUMOSTRUC3D (van Breugel, 1991; Koenders, 1997; Ye, 2003). The nanostructures of inner and outer C-S-H are simulated by the packing of monosized (5 nm) spheres. The pore structures (capillary pores and gel pores) of Portland cement paste are established by upgrading the simulated nanostructures of C-S-H to the simulated microstructures of Portland cement paste. The pore size distribution of Portland cement paste is simulated by using the image segmentation method (Shapiro and Stockman, 2001) to analyse the simulated pore structures of Portland cement paste. The simulation results indicate that the pore size distribution of the simulated capillary pores of Portland cement paste at the age of 1 day to 28 days is in a good agreement with the pore size distribution determined by scanning electron microscopy (SEM). The pore size distribution of the simulated gel pores of Portland cement paste (interlayer gel pores of outer C-S-H and gel pores of inner C-S-H are not included) is validated by the pore size distribution obtained by mercury intrusion porosimetry (MIP). The pores with pore size of 20 nm to 100 nm occupy very small volume fraction in the simulated Portland cement paste at each curing time (0.69% to 1.38%). This is consistent with the experimental results obtained by nuclear magnetic resonance (NMR)

Co-processing of raw and washed air pollution control residues from energy-from-waste facilities in the cement kiln

Co-processing of industrial wastes as alternative raw materials in cement manufacture is an example of industrial symbiosis for improved material resource efficiency. Since co-processing introduces impurities from wastes, such as air pollution control residue (APCR) from municipal solid waste combustion, into the cement kiln, a better understanding of their environmental impacts and effects on cement manufacturing and quality is needed. Portland cement clinkers containing 5–35% raw or 5–34% washed APCR were prepared, with formation of all typical minerals, but with effects on clinkering reactions, and increased 2CaO·SiO2 and decreased 3CaO·SiO2 and 3CaO·Al2O3. Raw APCR affected the shape of the 2CaO·SiO2 and 3CaO·SiO2 grains, and cement paste from clinker made with 35% APCR exhibited negligible 28d strength. Pastes from the clinkers with lower contents of APCR or washed APCR had strengths that were lower than that of the control at 7d, similar at 28d (∼90 MPa) and higher at 6 m (up to 120 MPa), consistent with their 2CaO·SiO2 and 3CaO·SiO2 contents. Utilization of minerals in APCR thus comes with a trade-off against cement quality. Volatilisation of S, Cl, Pb was reduced by washing, which fully eliminated volatilisation of Zn. Zn was found mainly in the interstitial phases of the clinker, in solid solution in 4CaO·Al2O3·Fe2O3 or 3CaO·Al2O3. Further investigation is required to determine whether Zn and other incorporated elements may be released from the cement paste when these phases react with water. APCR co-processing may reduce CO2 emissions by avoiding CaCO3 decomposition, but this is an uncertain benefit, which may be outweighed by the detrimental effects of APCR alkalis, Cl, S and metals on cement production and quality. Life cycle environmental impacts associated with washing, and dispersal of contaminants in the built environment through construction materials, are additional concerns

Linking the SO2 emission of cement plants to the sulfur characteristics of their limestones: A study of 80 NSP cement lines in China

In a properly operated new suspension preheater (NSP) cement line, the SO2 emission is mainly originated from sulfides in the raw meal, and limestone, occupying about 85% wt. of the raw meal, is the dominant sulfur source. However, the sulfur characteristics of limestones and then their influences on the SO2 emission have not been clarified yet. In the present study, 80 NSP cement lines with SO2 emission > 200 mg/Nm3 were recorded, the sulfur content and species as well as pyrite morphology of limestones were analyzed and then correlated to their resulting SO2 emission. The results show that the SO2 emission of stack gas increases linearly with the SO3 content of limestone used, and sulfates lead to a 50% reduction in SO2 emission relative to sulfides. Compared with average SO2 emission, euhedral pyrite leads to a slightly higher SO2 emission, whereas metasomatic pyrite results in a lower SO2 emission, which can be attributed to the effects of accompanying elements (Ti, F, K, and Al etc.) on the desulfurization reaction and clinkerization in the whole NSP cement line. The relationships proposed can be used to predict the SO2 emission based on the sulfur characteristics of limestone and to rationally utilize high-sulfur limestone in cement industry

Bond-Slip Behavior of Basalt Fiber Reinforced Polymer Bar in Concrete Subjected to Simulated Marine Environment: Effects of BFRP Bar Size, Corrosion Age, and Concrete Strength

Basalt Fiber Reinforced Polymer (BFRP) bars have bright potential application in concrete structures subjected to marine environment due to their superior corrosion resistance. Available literatures mainly focused on the mechanical properties of BFRP concrete structures, while the bond-slip behavior of BFRP bars, which is a key factor influencing the safety and service life of ocean concrete structures, has not been clarified yet. In this paper, effects of BFRP bars size, corrosion age, and concrete strength on the bond-slip behavior of BFRP bars in concrete cured in artificial seawater were investigated, and then an improved Bertero, Popov, and Eligehausen (BPE) model was employed to describe the bond-slip behavior of BFRP bars in concrete. The results indicated that the maximum bond stress and corresponding slip decreased gradually with the increase of corrosion age and size of BFRP bars, and ultimate slip also decreased sharply. The ascending segment of bond-slip curve tends to be more rigid and the descending segment tends to be softer after corrosion. A horizontal end in bond-slip curve indicates that the friction between BFRP bars and concrete decreased sharply

Optimization of the MgO-SiO₂ binding system for fiber-cement production with cellulosic reinforcing elements

A range of MgO and SiO2 blends mixed with water are analyzed to develop clinker-free fiber-cement products reinforced with cellulosic fibers. The target is the development of a binder which is not chemically aggressive to the fibers, but which develops high mechanical strength Mechanical performance of the materials developed is not only influenced by magnesium silicate hydrate (M-S-H) gel content, but is more related to the void content within the paste due to unreacted water, meaning that the gel-space ratio concept is valuable in describing the compressive strengths of these materials. A higher MgO content in the mix formulation leads to M-S-H gels with increased Mg/Si ratio. The Mg/Si ratio also increases over time for each mix, indicated by changes in the gel structure as reaction is not yet complete after 28 days. SEM shows a heterogeneous microstructure which also has regions of high Si content. The 60 wt%MgO-40 wt%SiO2 system is chosen as the optimal formulation since it is the least alkaline binder with high mechanical strength. Bending tests on pastes reinforced with cellulosic pulps prove the efficiency of this binder, which preserves the reinforcing capacity of the fibers much better than Portland cement pastes after 200 cycles of accelerated ageing

An efficient 3D point cloud data denoising algorithm for ship block visual measurement

For the 3D point cloud data aquired by laser scanning measurement of ship block, an efficient denoising algorithm based on image and normal vector threshold judgement is proposed. Firstly, large scale noise points are eliminated using global threshold judgement based image, then Kuwahara filter algorithm is used for data smoothing and a denoising algorithm based on normal vector threshold judgement is proposed to eliminate noises point excluding ship manufacture sections. The experiment result demonstrates that not only the proposed denoising algorithm keeps key data points but also avoids bluring point cloud boundary and eliminates noise points effectively

Preparation of Nano - SiO₂ Modified Waterborne Polyurethane Coatings and Its Influence on the Anti - Permeability of Concrete

For improving the anti-permeability of waterborne polyurethane coatings to concrete,the silane coupling agent was applied to modify the surface of nano-SiO2 to reduce the reunion degree of nanoparticles,and then the modified nano-SiO2 with better dispersibility was added into the waterborne polyurethane coatings.The modification effect of silane coupling agent on nano-SiO2 was analyzed by thermal analysis (TG),infrared spectroscopy (FT-IR) and dynamic light scattering (DLS),and the effect of nano-SiO2 on the morphology and composition of waterborne polyurethane coatings was also expounded.Furthermore,the influence of nano-SiO2 modified waterborne polyurethane coatings on the anti-permeability of concrete was analyzed.Results showed that the nano-SiO2 modified by silane coupling agent possessed less-OH on the surface and a lower reunion degree.Comparing with the concrete specimens painted with the polyurethane coatings containing no SiO2 or unmodified nano-SiO2,the concrete specimen painted with polyurethane coating containing modified nano-SiO2 had stronger adhesion between the coating and the concrete.The capillary water absorption per unit area of the specimen and the penetration depth of chloride ions were reduced,and the permeability resistance of the concrete was improved

Exploring Ho substituted Y-Fe-B nanocrystalline alloys and hot worked magnets

Aiming to balance the utilization of rare earth (RE) resources and develop Y-Fe-B based permanent magnets, Ho is employed as strategic substitution for enhancing the magnetic properties and thermal stability of nanocrystalline Y-Fe-B alloys. Ho substituting Y can enhance the coercivity of Y-Fe-B alloys while maintaining their excellent thermal stability. 30 at.% Ho substitution leads to an abnormal increase of remanence J _r and (Y _0.7 Ho _0.3 ) _2 Fe _14 B alloy exhibits good magnetic properties with remanence J _r = 0.73 T, intrinsic coercivity H _cj = 303 kA m ^−1 , and maximum energy product ( BH ) _max = 66 kJ m ^−3 . High thermal stability with temperature coefficient of remanence α = −0.124%/K and temperature coefficient of coercivity β = −0.245%/K were obtained between 300–400 K. The results for RE-rich (Y _1−x Ho _x ) _2.5 Fe _14 B alloys also show that the magnetic properties change with Ho content are similar to those of (Y _1−x Ho _x ) _2 Fe _14 B alloys, but the coercivity is higher. In addition, nanocrystalline (Y _0.5 Ho _0.5 ) _2.5 Fe _14 B magnets were prepared by hot-pressing and hot deformation process. Due to the lack of low melting point RE-rich phase, this alloy is difficult to be densified and deformed. The formation of high temperature RE _2 O _3 and RE _6 Fe _23 phases and the lack of continuously distributed RE-rich grain boundary phase are responsible for the poor texture of hot deformed magnet. The hot deformed magnet has the magnetic properties of J _r = 0.50 T, H _cj = 739 kA m ^−1 , and ( BH ) _max = 40 kJ m ^−3 together with high thermal stability. The micro-analysis demonstrated the chemical segregation of Y and Ho elements. Higher proportion of Ho than Y existed in main phase and grain boundary phase indicate excess Y were precipitated as Y-rich oxides

Hybrid Effect of Wollastonite Fiber and Carbon Fiber on the Mechanical Properties of Oil Well Cement Pastes

Oil well cement is a type of natural brittle material that cannot be used directly in cementing operations. Fiber is a type of material that can effectively improve the strength and toughness of cement stone, and hybrid fiber materials can more effectively improve the performance of a cement sample. To overcome the natural defects of oil well cement, the new mineral fiber, i.e., wollastonite fiber, and common carbon fiber were used in oil well cement, and the micromorphology, mechanical properties, and stress-strain behavior of the cement were evaluated. The experimental results show that carbon fiber and wollastonite fiber are randomly distributed in the cement paste. The mechanical properties of the cement paste are improved by bridging and pulling out. The compressive strength, flexural strength, and impact strength of cement stone containing only carbon fiber or wollastonite fiber are higher than those of the pure cement, but too many fibers are not conducive to the development of mechanical properties. A mixture of 0.3% carbon fiber with 6% wollastonite fiber in oil well cement slurry results in a greater increase in compressive strength, flexural strength, and impact strength. In addition, compared with blank cement stone, the strain of the mixed cement stone increases substantially, and the elastic modulus decreases by 37.8%. The experimental results supply technical support for the design of a high-performance cement slurry system