Influence of moisture- and CO₂- induced ageing in cement on the performance of admixtures used in construction chemistry

1 Appearance of the cement samples that had been exposed to moisture after storage for a) 1 day and b) 3 days

2 Scanning electron microscope photomicrographs of the CEM I 52,5 N cement a) in the fresh state, and after exposure to moisture for b) 1 day and c) 3 days

3 FTIR-ATR spectra of fresh (black) and pre-hydrated CEM I 52,5 N cement
(blue: exposure time 1 d; red: 3 d)

4 Thermogravimetric analysis of fresh CEM I 52,5 N cement (green) and of cement stored in moist conditions (blue: storage time 1 d; red: 3 d)

5 Hydration behaviour of fresh CEM I 52,5 N cement (green) and of cement that has been exposed to moisture (blue: storage time 1 d; red: 3 d), determined by thermocalorimetry

6 Zeta potential of cement pastes (w/c = 0.55) made from fresh (green) and pre-hydrated CEM I 52,5 N cement (blue: storage time 1 d; red: 3 d)

7 Flow table spread of cement pastes (w/c = 0.55) made from fresh (green) and pre-hydrated CEM I 52,5 N cement (blue: storage time 1 d; red: 3 d) with and without superplasticizer

8 Water retention of pastes made from fresh (green) and pre-hydrated cement on addition of different levels of MHEC (blue: storage time 1 d; red: 3 d)

9 Appearance of the cement paste after the water retention test; left: cement pre-hydrated for 1 day containing 0.3 mass % MHEC; right: cement pre-hydrated for 3 days containing 0.2 mass % MHEC

10 Setting behaviour of cement pastes made from fresh (green) and pre-hydrated CEM I 52,5 N cement (blue: storage time 1 d; red: 3 d) in the presence of 0.9 mass % Al₂O₃-based accelerator (left) and 1 mass % calcium formate (right)

Cement may exhibit altered properties during extended storage in moist atmospheres. It is assumed that these effects are attributable to the take-up of atmospheric humidity and to carbonation at the surfaces of the cement particles.

1 Introduction

Cement may be affected by moisture and become slightly hydrated on the surface due to sorption of water both during production and during transport and subsequent storage in contact with atmospheric humidity [1 – 4]. Water vapour and possibly also CO₂ react with the surface of the cement particles. The surface hydration may even begin during the production in the cement plant, e.g. as a consequence of the dehydration of gypsum during the grinding process in the cement mill. Some cement producers also spray up to 2 % water into the clinker mill in order to keep the temperature...