CEMENT AND CONCRETE RESEARCH(2022 - 2022)
Effect of magnesium silicate hydrate (M-S-H) formation on the local atomic arrangements and mechanical properties of calcium silicate hydrate (C-S-H): In situ X-ray scattering study
Kim G., Im S., Jee H., Suh H., Cho S., Kanematsu M., Morooka S., Koyama T., Nishio Y., Machida A., Kim J., Bae S.
CEMENT AND CONCRETE RESEARCH, Elsevier Ltd., Vol.159, 2022, .
(https://doi.org/10.1016/j.cemconres.2022.106869)
Abstract
This study explored the effect of M-S-H formation on the local atomic arrangements and mechanical properties of C-S-H. The elastic moduli of the samples were calculated using shifted atomic distances (r) and d-spacings (d) acquired by applying an external load on the pastes during X-ray scattering experiments. The experimental results indicated that the crystal structure of C-S-H remained intact with MgCl2 addition. At the highest Mg/Si ratio (Ca/Si = 0.6, Mg/Si = 0.2), change in the dominant phase occurred from C-S-H to M-S-H because the low pH environment hindered the formation of C-S-H and facilitated the formation of M-S-H. The elastic modulus decreased with increasing Mg/Si ratio up to 0.1 owing to both C-S-H destabilization and low M-S-H content in the samples. Conversely, the elastic modulus increased in the paste synthesized with the highest Mg/Si ratio because considerable M-S-H had formed, which exhibited a higher elastic modulus than C-S-H. c 2022 Elsevier Ltd
Surface area development of Portland cement paste during hydration: Direct comparison with 1H NMR relaxometry and water vapor/nitrogen sorption
Kurihara R., Maruyama I.
CEMENT AND CONCRETE RESEARCH, Elsevier Ltd., Vol.157, 2022, .
(https://doi.org/10.1016/j.cemconres.2022.106805)
Abstract
The specific surface areas of sealed-cured hardened cement pastes (HCP) were evaluated during the hydration process using three types of Portland cement and with two different water-to-cement ratios. The BET surface area was measured by water vapor/nitrogen sorption and directly compared with that obtained by the fast exchange model measured by 1H NMR relaxometry. The results confirmed that the total surface area evaluated by 1H NMR was consistently 2?2.5 times larger than the water vapor BET surface area for different HCPs. This difference is attributed to the local stacking of C-S-H layers: the surface between adjacent stacked layers is not measurable by water vapor due to the nature of the pre-treatment, while 1H NMR is able to measure the entire interlayer surface. The nitrogen surface area is better able to include the majority of the HCP gel pore surface by 1H NMR for white and high-early-strength Portland cement. c 2022 The Authors
40 years of PCE superplasticizers - History, current state-of-the-art and an outlook
Lei L., Hirata T., Plank J.
CEMENT AND CONCRETE RESEARCH, Elsevier Ltd., Vol.157, 2022, .
(https://doi.org/10.1016/j.cemconres.2022.106826)
Abstract
2021 marks the 40th year since polycarboxylate superplasticizers (PCEs) have been invented by Nippon Shokubai company in Japan. This invention clearly represents a major breakthrough and milestone in modern concrete technology. In this review article, at first Dr. Hirata ? the main inventor of PCE superplasticizers ? reports on the history behind their invention and market entry. Thereafter, recent developments and innovations in PCE technology are presented. As of today, the market offers a wide range of chemically different PCE products, among them HPEG and IPEG PCEs have occupied the largest market share because of their superior cost-effectiveness. At this moment, novel types of PCEs including EPEG and GPEG PCEs are being introduced, thus enriching the family of vinyl ether (VPEG) superplasticizers. In spite of the huge success of PCEs, also challenges in specific applications such as their sensitivity towards clay contaminants or the viscous (gstickyh) flow behavior of concrete mixed at low w/c ratios became obvious and will be addressed. Furthermore, as the concrete industry currently undergoes a fundamental transition to low-carbon binders in order to reduce anthropogenic CO2 emission, PCE superplasticizers suitable for such low or zero clinker binders including calcined clay blended cements or alkali activated slags are being sought and the current state-of-the-art in this field will be discussed. Finally, the future perspectives of PCE technology in a dramatically changing industry are assessed and the pivotal role of PCEs in this mega transition faced by the construction industry will be pointed out. c 2022 Elsevier Ltd