Publications

Understanding the role of curing conditions on the microstructure and phase chemistry of alkali-activated materials (AAMs) is essential for the evaluation of the long-term performance as well as the optimization of the processing methods for achieving more durable AAMs-based concretes. However, this information cannot be obtained with the common material characterization techniques as they often deliver limited information on the chemical domains and proportions of reaction products. This paper presents the use of PhAse Recognition and Characterization (PARC) software to overcome this obstacle for the first time. A single precursor (ground granulated blast-furnace slag (GBFS)) and a binary precursor (50% GBFS–50% fly ash) alkali-activated paste are investigated. The pastes are prepared and then cured in sealed and unsealed conditions for up to one year. The development of the microstructure and phase chemistry are investigated with PARC, and the obtained results are compared with independent bulk analytical techniques X-ray Powder Fluorescence and X-ray Powder Diffraction. PARC allowed the determination of the type of reaction products and GBFS and FA’s spatial distribution and degree of reaction at different curing ages and conditions. The results showed that the pastes react at different rates with the dominant reaction products of Mg-rich gel around GBFS particles, i.e., Ca-Mg-Na-Al-Si, and with Ca-Na-Al-Si gel, in the bulk paste. The microstructure evolution was significantly affected in the unsealed curing conditions due to the Na+ loss. The effect of the curing conditions was more pronounced in the binary system.

In this research, self-healing due to further hydration of unhydrated cement particles is taken as an example for investigating the effects of capsules on the self-healing efficiency and mechanical properties of cementitious materials. The efficiency of supply of water by using capsules as a function of capsule dosages and sizes was determined numerically. By knowing the amount of water supplied via capsules, the efficiency of self-healing due to further hydration of unhydrated cement was quantified. In addition, the impact of capsules on mechanical properties was investigated numerically. The amount of released water increases with the dosage of capsules at different slops as the size of capsules varies. Concerning the best efficiency of self-healing, the optimizing size of capsules is 6.5 mm for capsule dosages of 3%, 5%, and 7%, respectively. Both elastic modulus and tensile strength of cementitious materials decrease with the increase of capsule. The decreasing tendency of tensile strength is larger than that of elastic modulus. However, it was found that the increase of positive effect (the capacity of inducing self-healing) of capsules is larger than that of negative effects (decreasing mechanical properties) when the dosage of capsules increases.

reduce CO2 emission as well. The fine limestone powder may accelerate the early hydration of cement clinkers by providing extra nucleation sites; Furthermore, inert limestone filler can further influence the later compressive strength due to two different effects, the dilution effect (strength reduction) and the filler effect (better packing of the powder; strength increase). In this study, the content of blast-furnace slag in a slag blended cement (cement:slag=0.3:0.7, by mass) is reduced from 70% to 60% by the replacement of 10% limestone powder, aiming to make a ternary blended cement to further reduce CO2 emission. The compressive strength of mortar (cement:slag:limestone:water:sand = 0.3:0.6:0.1:0.5:3, by mass) tested according to European Standard EN 196-1:2005 shows that the addition of limestone filler increases the compressive strength of ternary blended cement from 1 up to 180 days. Investigation indicates that the positive effect of limestone addition on compressive strength is caused by the increased hydration of Portland cement on the one hand, and the hindered transformation of ettringite to monosulphate in the presence of limestone on the other. The result may give us more information to produce even greener cementitious materials using limestone filler.

At present, the indirect method is applied to measuring and controlling mechanical compressive stress, which is the measurement and control of rotating torque of screw with torque transducer during screw revolving. Because the friction coefficient between every screw-cap and washer, of screw-thread is different, the compressive stress of every screw may is different when the machinery is equipped. Therefore, the accurate measurement and control of mechanical compressive stress is realized by the direct measurement of mechanical compressive stress. The author introduces the research of contrast between compressive stress and rotating torque in the paper. The structure and work principle of a special washer type transducer is discussed emphatically. The special instrument cooperates with the washer type transducer for measuring and controlling mechanical compressive stress. The control tactics based on the rate of compressive stress is put to realize accurate control of mechanical compressive stress.

Durability of materials and structures is one of the key-components of sustainable development. Premature failures due to any kind of degradation gives rise to expensive repair or, in the worst case, complete demolition of a structure. The indirect costs of repair due to process or traffic interruptions may easily exceed 5 to 10 times the direct costs. Premature failure of aging materials and structures and, hence, a shorter service life, also means higher impact on the environment and a negative contribution to the development of a sustainable society. Degradation of materials and structures finds its origin in infinitesimal small changes and instabilities at the atomic, nano and microscale of a material. These are the levels at which aging phenomena start. This is at least one way to look at durability and sustainable issues. In 2008 this way of looking at the problem had inspired the school of Materials Sciences & Engineering of Southeast University in China and the section Materials & Environment of Delft University of Technology to organize the first International Conference on Microstructure Related Durability of Cementitious Composites in Nanjing. The conference became a success and it was decided to organize a second conference, Microdurability’2012, in Amsterdam. The response to the call for papers for this second conference was overwhelming. Over 260 abstracts were submitted, finally resulting in almost 190 papers. Attendants from more than 40 countries have subscribed to the conference, representing all continents. This response convincingly illustrates the relevance of the topic and the interest of researchers and other stakeholders to participate in the durability debate. Microdurability’2012 is a Sino-Dutch initiative organized under the umbrella of RILEM and is also supported by ACI. The organizers would like to thank both RILEM and ACI for adopting this conference. From the Chinese side both Southeast University and Jiangsu Research Institute of Building Science participated in organizing this conference, whereas from the Dutch side Delft University of Technology was involved. Since the conference takes place in The Netherlands, it is clear that most of the work for organizing this event was carried by staff members and PhD students from the TU Delft. The enthusiasm and perseverance of the key-persons in the organization, Mrs. Iris Batterham and dr. Ye Guang and their team was enormous and is gratefully acknowledged here. On behalf of the Organizing Committee we would finally like to thank all the keynote speakers, the Scientific Committee, authors and delegates for their collaboration and presence in this conference. The support from companies, who have sponsored the conference, is gratefully acknowledged. We wish you all most fruitful discussions during this conference, a wonderful stay in Amsterdam and unforgettable visits to typically Dutch places in Amsterdam’s neighborhood.