CEMENT最新文献

The use of biomass ash is an environmentally friendly practice in the search for sustainable construction materials. This study aimed to produce pozzolanic ash from corn straw with a high amorphous silica content, low carbon content, and high specific surface area via controlled acid leaching, two-step burning, and grinding. The effect of pretreating corn straw on the properties of the material was assessed by comparative analysis with corn straw and rice husk ashes produced without acid pretreatment. To this end, characterization data, hydration heat, chemically bound water, and portlandite consumption in pastes, and mortar compressive strength were used to evaluate the pozzolanicity of the ashes. The results indicated that all the ashes exhibited pozzolanic behavior and that the leaching process significantly improved the physical and chemical properties of corn straw ash, with reduction in portlandite content. The calorimetric results showed a change in hydration kinetics with an increase in ash in the cement mixes. Moreover, the compressive strength of leached corn straw ash-based mortars was greater than that of the other mortars, primarily for high levels of cement replacement (20 and 30% by mass).

Hydrates are significant components of cements and concrete. We examine the effective volumes of waters of crystallization for these materials, where the “effective volumes” are the difference per water molecule between the formula volume of the hydrate and of its parent anhydrate. These effective volumes cover a small range around 15 cm³ mol⁻¹ (≅ 23 ų per water molecule), unlike the wider range for general inorganic materials.

We also examine the thermodynamic properties of the cementitious phase, which follow the generally observed correlation of relating to their molar volumes. We establish “effective” additive oxide parameters for enthalpy and for molar volume, which are useful in confirming experimental values and in predicting as-yet undetermined values. Their Debye temperatures approximate to 600 K; this Debye temperature is well above ambient temperature and suggests that the vibrational modes of these cementitious phases are only partially excited and that the materials are hard. Ferrate-containing materials generally have a lower Debye temperature (∼273 K) implying that they may be softer than other cementitious materials.

These observations may be useful in checking for errors in data and anomalies in behavior among related cementitious materials.

The Damage Rating Index (DRI) has been increasingly used in North America since it answers interesting questions on the cause and extent of damage in concrete. Currently, the DRI is mostly used to appraise alkali-silica reaction (ASR) affected concrete and there is very few research on the evaluation of other distress mechanisms through this method. This work presents the use of the DRI to assess condition of concrete affected by internal swelling reaction (ISR) mechanisms (i.e. ASR, delayed ettringite formation and freeze-thaw cycles), with the aim of verifying the suitability of the method to become a comprehensive damage evaluation protocol. Results show that the DRI number, represented by plots or bar charts, enables a quantitative damage evaluation of concrete regardless of the distress mechanism type and degree. Moreover, the implementation of an extended DRI version makes the method more suitable to describe progress of different ISR deterioration processes in concrete.