Xiulin Huang

Effect of curing regime on degree of Al3+ substituting for Si4+ in C-S-H gels of hardened Portland cement pastes

The effect of curing regime on degree of Al3+ substituting for Si4+ (Al/Si ratio) in C-S-H gels of hardened Portland cement pastes was investigated by 29Si magic angel spinning (MAS) nuclear magnetic resonance (NMR) with deconvolution technique. The curing regimes included the constant temperature (20, 40, 60 and 80 °C) and variable temperature (simulated internal temperature of mass concrete with 60 °C peak). The results indicate that constant temperature of 20 °C is beneficial to substitution of Al3+ for Si4+, and Al/Si ratio changes to be steady after 180 d. The increase of Al/Si ratio at 40 °C is less than that at 20 °C for 28 d. The other three regimes of high temperature increase Al/Si ratio only before 3 d, on the contrary to that from 3 to 28 d. However, the 20 °C curing stage from 28 to 180 d at variable temperature regime, is beneficial to the increase of Al/Si ratio which is still lower than that at constant temperature regime of 20 °C for the same age. A nonlinear relation exists between the Al/Si ratio and temperature variation or mean chain length (MCL) of C-S-H gels, furthermore, the amount of Al3+ which can occupy the bridging tetrahedra sites in C-S-H structure is insufficient in hardened Portland cement pastes.

Effects of molecular structure of polycarboxylate-type superplasticizer on the hydration properties of C3S

Effects of polycarboxylate-type superplasticizer (PC) molecular structure on the hydration heat of tricalcium silicate (C3S) paste and polymerization degree of hydration products (C-S-H gel) were researched by using TAM AIR isothermal microcalorimetry (TA) and 29Si nuclear magnetic resonance (NMR). Methoxy polyethylene glycol-methacrylates-based polycarboxylate superplasticizers with different side chain lengths and main chain lengths were employed. PC molecules with shorter main chain or longer side chains caused stronger retardation of C3S early hydration and lesser increase of C3S 3 d hydration degree. NMR measurement indicated that the incorporation of PC increased the hydration degree of C3S paste and the polymerization degree of silicon-oxygen tetrahedron of C-S-H gel. The tendency for C3S 7 d hydration degree to improve was more pronounced while PC molecules with longer main chain or shorter side chain were added. Whereas, PC molecules with longer main chains or longer side chains increased the 7 d polymerization degree of C-S-H gel.

Effect of curing regime on polymerization of C-S-H in hardened cement pastes

The effect of two different curing regimes on the polymerization degree of C-S-H in hardened cement pastes within 28 d were investigated by measuring the chemical environments of 29Si with magic angle spinning (MAS) nuclear magnetic resonance (NMR) and by analyzing the 29Si NMR spectra with deconvolution technique. The experimental results indicate that, at curing regime of constant temperature of 20 °C, the polymerization of C-S-H increases and then decreases with curing age, and the Al/Si ratio increases gradually with curing age, furthermore, the two non-bridging oxygen bonds of bridging silicate tetrahedra in C-S-H structure mainly bond to H+. At curing regime of variable temperature, the polymerization of C-S-H firstly increases then changes slightly and subsequently decreases with the temperature from low to high and then to low, and the Al/Si ratio firstly increases then keeps invariant and subsequently slightly decreases. Moreover, the temperature decreasing is advantageous for the Ca2+ to be bonded to the bridging silicate tetrahedra and entering into the interlayer of C-S-H structure. The polymerization of C-S-H at curing regime of variable temperature is higher than that cured at constant temperature, but the curing regime of constant temperature is more beneficial to the substitution of Al3 for Si4+ than that of variable temperature.

Effect of curing regime on the distribution of Al3+ coordination in hardened cement pastes

The effect of curing regime on the distribution of Al3+ coordination in hardened cement pastes within 28 d were investigated by 29Si and 27Al magic angle spinning (MAS) nuclear magnetic resonance(NMR) with deconvolution technique. The results indicate that the tetrahedral coordination Al3+ incorporated in C-S-H structure mainly originate from the Al3+ incorporated in the alite and belite phases in the Portland cement. The curing regime of constant temperature of 20 °C is beneficial to the octahedral coordination Al3+ transforming to tetrahedral coordination Al3+ incorporated in C-S-H structure. However, at curing regime of variable temperature, the temperature rising process is more advantageous to the transformation from ettringite to monosulphate, substitution of Al3+ for Si4+ in the C-S-H structure and the formation of the third aluminate hydrate (TAH) than that at constant temperature of 20 °C. The high temperature of 60 °C in the holding temperature process promotes the decomposition of ettringite, and enhances the consumption of the Al3+ incorporated in C-S-H phases and the Al3+ in TAH for the monosulphate forming. The temperature decreasing promotes the transformation from monosulphate to ettringite, and increases the consumption of the Al3+ incorporated in C-S-H phases, and then increases the quantity of the TAH.

Radiation shielding performance of aggregates made by sludge with high content of heavy metal

A new method to prepare radiation shielding functional aggregate is described, and an appropriate mix ratio and a reasonable calcinated condition was engaged. The γ-ray shielding capability of both the new functional aggregates and some other nature aggregates had been measured. The linear attenuation coefficients (µ, cm−1) of these aggregates had been calculated at photon energies from 1 keV to 10GeV using XCOM program, and measured at the photon energies of 662 keV, showing good agreement between experimental and calculated results. The results show that the γ-ray shielding capacity of the new functional aggregates has been improved substantially compared with basalt, almost equal to serpentine and high-titanium slag, and up to 80% to barite.