Methacrylate ester as well as allylether based polycarboxylates (PCEs) were synthesized to plasticize pastes of cement and silica fume having a water/cement ratio of 0.22. Methacrylate ester copolymers were found to disperse cement well, whereas allylether copolymers are more effective with silica fume. Mechanistic investigations revealed that in cement pore solution, the surface charge of silica fume becomes positive by adsorption of Ca 2+ onto negatively charged silanolate groups present on the silica surface. This way, polycarboxylate copolymers adsorb to and disperse silica fume grains. Thus, mixtures of both copolymers were tested in cement-silica fume pastes. These blends provide significantly better dispersion than using only one polymer. Apparently, the surfaces of hydrating cement (here mainly ettringite) and silica fume are quite different with respect to their chemical composition. Therefore, PCEs with different molecular architectures are required to provide maximum coordination with calcium atoms present on these surfaces.

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Interaction between polycarboxylate (PCE) comb polymers and microsilica suspended in a highly alkaline, Ca2+‐loaded model cement pore solution was studied via zeta potential, adsorption, and paste flow experiments. Zeta potential measurements reveal that in an alkaline suspension, microsilica possesses a negative surface charge stemming from deprotonated silanolate groups. Addition of soluble calcium salts (e.g., CaCl2) was found to cause a charge reversal to positive, owing to the adsorption of Ca2+ ions forming a monolayer on the microsilica surface. Further experiments demonstrate that through Ca2+ mediation, anionic PCE graft polymers adsorb in high amount on the microsilica surface. Polymers possessing a stronger anionic character exhibit a higher affinity to the positive microsilica surface, and consequently, exercise a more powerful dispersing effect than PCE showing less anionic character. A model summarizing the processes occurring at the surface of microsilica in this fluid system is proposed. The study suggests that the high fluidity of concrete containing microsilica depends on the effective dispersion of microsilica, and not of cement.

Precipitated silica Koestrosol 1530 is the basis for the recently adopted certified reference material ERM‐FD100 used for nanotechnology. A similar reference material based on another precipitated silica (silica Ludox™) has been used for testing ultrasound based instruments for particle sizing and zeta potential in concentrated dispersions and emulsions for the past two decades. In this study we test silica Koestrosol as a potential replacement for the silica Ludox™ since the latter has not been certified. The measurements were performed using ultrasound based instruments, which were suitable for concentrated systems. Two laboratories (USA and Germany) with 3 different instruments were involved, measuring samples at 5 % mass fraction. Samples mass fraction was 5 %. The statistically averaged mass‐based median particle size was found to be 22.4 ± 0.5 nm, which is within range of certified values obtained for more diluted samples. Values for ζ‐potential were measured as –26.7 ± 0.9 mV, with precision that is order of magnitude better then reported before.

Carbon capture and storage (CCS) is considered to be one of the most effective ways to dispose of CO2 generated in coal or gas fired power plants. Cementing such CCS wells presents a technical challenge since ordinary Portland cement (OPC) is known for its corrosion potential with CO2. Such corrosion involves formation and crystallization of CaCO3 from Ca(OH)2 which is formed during the hydration of cement. Furthermore, CaCO3 can be leached as Ca(HCO3)2. This process can create channels in the cementitious matrix for CO2 migration to the surface. Here, three Portland cement based systems were formulated with different mineral and chemical admixtures and compared with a common API Class G oil well cement with respect to CO2 stability. The systems investigated were based on various concepts. For one cementing system, the aim was to fill the pore space in the cementitious matrix with inorganic, CO2 inert particles while the second was treated with a number of chemical admixtures, particularly latex polymer, to achieve the same goal. The third system was based on slag cement (CEM III) formulated with fly ash. Hardened specimens (30×50 mm) of the four cementing systems were prepared and stored under supercritical CO2 at 90 °C and 400 bar for one and six months, respectively. The autoclave was half filled with a synthetic reservoir fluid, thus allowing storage in a CO2 saturated salt brine and in wet supercritical CO2 atmosphere. Ingress of CO2 into the hardened cement specimens was probed via phenolphthalein test. From all systems, only the slag cement (CEM III) blended with a reactive filler (fly ash) exhibited good CO2 resistance. This cement contains a specific ratio of SiO2:CaO which produces only a minor amount of portlandite which can carbonate. For the other cement samples, severe corrosion was observed. The cement system containing chemical admixtures and the neat API Class G system even exhibited severe cracking as a result of high crystallization pressure during CaCO3 growth. Still, carbonation rates were relatively low (~ 0.5 m/year). The major finding of this study is that common API oil well cement sufficiently withholds CO2 attack if formulated in such way that only minor amounts of CaCO3 are formed, and if the w/c ratio is high enough to provide sufficient pore space for expansion of CaCO3 crystals.