Dynamic mechanical measurements on portland cement pastes during setting and hardening

Abstract

Changes occurring in the dynamic mechanical properties of a Portland cement paste during setting at 21° to 22°C are presented for a sample with a water/cement ratio of 0.336. The dependence of the complex shear compliance, J ∗ = J′ - iJ″ , for this viscoelasti material on both time after wet mix and the frequency of the small-amplitude sinusoidal shear oscillations used is adduced. Comparisons are made of the dynamic mechanical behavior for paste measured during set and that of paste samples from the same mix allowed to set and harden before testing; the elastic compliance level ( J′) of the paste measured (and therefore vibrated in shear) during set is much less. The occurrence of sharp resonance dispersions at audiofrequencies (500 to 10,000 c/sec) for some of the samples is evident, and an apparent resonant frequency dependence on the micron-size diameters of the unhydrated cement particle cores is pointed out. These resonances and their time (particle size) dependence are in accord with previously advanced concepts on the existence of intrinsic momentum-wave modes in crystalline lattice segments. Suggestions for future dynamic mechanical measurements, and their probable relevance to both an increased understanding of the setting process and to nondestructive strength determinations, are also given.