By using XRD diffraction patterns and SEM scanning electron microscopy, the study included exploring the effects of carbonation on the types of cations, namely Na+ and Mg2+, on the chloride concentration and mechanism, which is an important factor that has received little attention. The results show that carbonization has a greater negative impact on the binding capacity of chloride ions in cement mixed with NaCl, and CaCl2 can weaken the negative effect of carbonization on the binding capacity of chloride ions and improve the binding capacity of free chloride ion ;During the carbonization of cement mixed with NaCl, the chloride content corresponding to the maximum chloride ion binding rate was reduced from 0.9 % to 0.8 %, while the value was 0.8 % in cement mixed with CaCl2;Carbonization can improve the structure of the cement and reduce the porosity in the cement structure.
Aiming at the bending performance of the prestressed superposing‐poured concrete beam, the numerical simulation on the composite beams poured with the normal weight concrete (NWC) superposed on the fibred ceramsite lightweight aggregate concrete (LWAC) was conducted. Three kinds of prestressing schemes, straight linear prestressing force, curved prestressing force not across the casting interface, and curved prestressing force across the casting interface, were simulated for comparison, and the influence of the casting interval time was also considered. Results indicate that the stiffness of the superposing‐poured beam can be effectively strengthened by considered schemes of the prestressing force; in addition, there are certain increases on the ultimate load except imposing the straight linear prestressing force. As the curved prestressing force is imposed across the casting interface, the maximal interlayer slip of the casting interfacial transition zone (C‐ITZ) approximately equals to that without the prestressing force. The scalar stiffness degradation (SDEG) of the C‐ITZ for the casting interval time being 14 days is obvious because of the weakening on the bonding performance of the C‐ITZ. Comparatively, the SDEG variation of the C‐ITZ in the model with the curved prestressing force across the casting interface is smoother and smaller on the whole than the other two prestressed schemes for the case of the casting interval time being 14 days.
In this paper, using sewage sludge carried out to manufacture high performance ceramsite.At the same time, the performance of concrete made from sewage sludge ceramsite was analyzed.The results show that the ceramist is mainly composed of cristobalite and mullet, and has dense enamel structure on surface and honeycomb closed fine porous structure in internal.Too large ceramsite size can cause concrete strength decrease, poor stability and workability; mineral admixtures make strength and workability of ceramsite concrete improve, but excessive addition could reduce concrete strength particularly in the early stage, so there is a reasonable dosage; ceramsite concrete strength is increased with the decrease of water-cement ratio, the increase of strength is not obvious when water-cement ratio reduced to a certain extent; increasing sand-ratio can improve concrete strength, but have adverse impact on the workability of fresh concrete.
Researched the mix proportion of using self-made high-performance sludge ceramic to prepare LC40 LWAC. Studied the effect of ceramic-size, supplementary cementitious materials, water-cement ratio and sand-ratio on the LWAC performance. The study shows, size of ceramic too large can cause strength decrease, poor stability and workability; supplementary cementations materials make strength and workability of LWAC improve, but excessive addition could reduce concrete strength particularly in the early stage, so there is a reasonable dosage; LWAC strength is increased with the decrease of water-cement ratio, but for the limit of strength of LWA, the increase of strength is not obvious when water-cement ratio reduced to a certain extent; increasing sand-ratio can improve concrete strength, but have adverse impact on the workability of fresh concrete. Using the study results, optimized the concrete mix proportion and prepared LC40 LWAC with density level 1700, slump degree over 18cm, extended degree over 50cm.
To solve rebar corrosion in existing concrete structures, two test methods, adding corrosion inhibitors into concrete and applying corrosion inhibitors on the existing concrete surface by brushing and pouring and composite repair, combined with natural potential, XRD and SEM, were used to comprehensively evaluate the performance of nitrite‐based compound corrosion inhibitors. The research results show that nitrite has a better inhibitory effect than phosphate, and when the respective mass fraction of hydrogen phosphate and sodium nitrite is about 1.5%, the rust inhibition effect is the optimum. Brushing, perfusion, and composite repair can all play a good role in inhibiting corrosion of which composite repair is the best. The addition of phosphate can improve the macrocell corrosion caused by the low dosage or uneven distribution of nitrite.
The experimental results are presented on the corrosion of reinforcing steel bars in the pore solutions of harden con-crete mortar with various anti-freezing admixtures with different concentrations of nitrite and chloride. The half-cell potentials, mass loss and corroded area of the reinforcing bars in the corrosion were measured for determination of the relationship between the ion concentration in the pore solution and the inhibition of corrosion. It is indicated that a higher nitrite content is, the high-er molar ratio of NO2-/Cl- is in pore solution, and the effective protection for the bars from corrosion in the mortar will be.
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