Pozzolana from minerals – State of the art. COIN P1 Advanced cementing materials and admixtures. SP 1.4F Alternative pozzolans

The objective of this state-of-the-art report (STAR) is to review work done to make pozzolana from natural occurring minerals by chemical treatment, and also outline principle possibilities of doing so. It does not include pozzolana by thermal treatment as for e.g. clays. Based on the theory of acidity of oxides a general principle for preparing pozzolana from a mineral has been forwarded; to present the basic oxide part of a “neutral” mineral for a more acidic chemical than its acidic oxide counterpart. Thus, the present STAR has reviewed the possibility of making pozzolana for cement and concrete by treatment with weak and strong acids. The most feasible minerals seem to be olivine and serpentine, both widely available in the Earths crust, and also with large deposits in Norway. The more seldom mineral Anorthite, but with a good deposit in Norway, is deemed less suitable since the pozzolana produced by strong acid attack retain the shape of the original mineral, unlike Olivine that falls apart to a fine powder. Thus, the relatively coarse grain pozzolana from Anorthite will react chemically, but there will be no physical effect of improved particle packing as for conventional silica fume and possibly by pozzolana from Olivine. The pozzolana from Anorthite also contains fine pores that will suck water and reduce workability of concrete mixes containing it. A new process is starting up for production of magnesium chloride in Porsgrunn, Norway, by SilMag Technology treating Olivine with hydrochloric acid. However, before the silica residue can be used as a pozzolana for reinforced concrete, the remaining chloride content must be reduced to an acceptable level. However, Olivine can also react with the weak carbonic acid (CO₂ in water) and form a mixture of magnesium carbonate and silica. This will solve the potential problem of chloride contamination. It may not be necessary to separate the two components for concrete applications as magnesium carbonate could act as excellent filler and the silica as pozzolana. An interesting aspect is to see the sequestering of CO₂ by Olivine in connection with the cement industry. A cement factory has a flue gas relatively rich in CO₂ (about 20 vol%). If olivine or serpentine is used to capture some of this, the resulting residue of magnesium carbonate and silica could be interground with clinker to form blended cement with a filler part (magnesium carbonate) and a pozzolana part (silica). Thus, it would enable a double principal CO₂ reduction from a cement plant. An alternative to make a blended cement (requires drying), is to deliver the resulting slurry to a ready mix concrete producer or a precast concrete element fabric. It is recommended that COIN cooperates with the new CO₂ absorption laboratory to be built at SINTEF/NTNU to make a combined CO2sequestering and pozzolana/filler production.