RESUMO
At present, it is known that when there is clay in concrete, polycarboxylates (PCE) will preferably adsorb in the clay, so that PCE cannot be fully combined with cement particles, which reduces the workability of the cement slurry. In this paper, a new type of maltitol-ammonium salt cationic (KN-lm) sacrificial agent (SA) has been successfully developed via a simple method, which makes PCE easier to bond with cement particles in the cement slurry containing clay. The effect of KN-lm on the fluidity of clay-containing cement paste is studied, and the experimental results show that KN-lm, as an efficient SA of cement slurry, makes PCE more compatible with clay-containing cement slurry, and increases the initial fluidity of cement slurry by about 19%. Further investigations of TOC, XRD, and zeta potential measurements reveal that a KN-lm ion is only preferably adsorbed into clay compared to PCE through electrostatic adsorption but without having any crystal structure change, thus resulting in good dispersion of cement particles. The addition of KN-lm plays an important role in hindering the hydration expansion of the clay by preferential electrostatic adsorption, which means PCE cannot easily insert into the interlayer of the clay.
RESUMO
El Niño-Southern Oscillation (ENSO) was identified as the dominant predictor for the Indian summer monsoon rainfall (ISMR) in the early 1900s. An apparent weakening of the ENSO-ISMR relationship has been observed since the 1970s. Here, we found a clear restoration of the ENSO-ISMR relationship since 1999/2000. This restoring relationship is closely linked to the interdecadal transition of ENSO evolution and the associated sea surface temperature anomalies (SSTAs) over the tropical Atlantic. During 1979-1997, summer ENSO events mainly continued from the previous winter, which can drive apparent Atlantic Niña SSTAs to offset ENSO's impact on ISMR and weaken the ENSO-ISMR relationship. In contrast, when ENSO events newly emerge from late spring, as they have done more recently during 2000-2018, the associated tropical Atlantic SSTAs are weak and shift to the tropical North Atlantic, which can offset the contribution of Atlantic Niña and reinforce the ENSO-ISMR relationship. We identified that the diversity of ENSO's evolution, continuing from the previous winter or emerging from late spring, is the dominant factor perturbing the ENSO-ISMR relationship in recent epochs, with tropical Atlantic SSTAs as the crucial bridge. This finding should be considered in our efforts to improve ISMR prediction.