Cement Energy and Environment

These phases are delineated by distinct time points; each signifying a change in the system. The end of the induction period (t1) is marked by rapid acceleration in hydration, measured as the decrease in total measurable water, and the start of the lTD. The end of the lTD (t2) coincides with the peak in hydration rate and the start of gel pore formation which stops (t3) at the same time as T2L and T2S peaks merge to produce an apparently monomodal distribution (Fig. 2) and the position of T2S peak starts to shift to lower T2 values. 3.3 Meaning of measurable water Water detected by the CPMG experiment must be sufficiently mobile such that interactions with the pore surfaces result in a transverse relaxation long enough to produce an echo signal following the first refocussing pulse. The decay times of hydrogen protons associated with chemically reacted water, such as that incorporated into the minerals ettringite and portlandite, are too short and the magnetization from these crystall ine structures cannot be refocused with an 180° pulse. For this reason , these contributions are lost in the CPMG experiment as hydration proceeds. Furthermore, any relaxation component shorter than the echo time (105 ~s) are also lost due to both the electronic limitations of the low field benchtop instruments and the magnetic inhomogeneity resulting from high levels of paramagnetic impurities in the OPC samples [20]. Water that has been incorporated into the C-S-H gel as interlayer water also appears to be not measured by our instrument, although this is less conclusive than for the mineral forms and will be discussed further below in Section 3.4. Hydration was characterized by a continual decrease in measurable water (Fig. 6), noting that no water loss due to evaporation was measured at the end of hydration. Water that has become unmeasurable due to reduced mobility resulting from incorporation into hydration products will be termed here as 'incorporated water' (IW). Also, we propose that the fraction of the initial total measureable water represented by incorporated water (IW%) is a measure of hydration degree. We also propose that IW comprises water incorporated into the minerals ettringite and portlandite, as well as a third solid component previously identified and proposed to be hydrogen protons contained within the C-S-H layers [17], and C-S-H interlayer water, since it was not possible to distinguish between them. Interpretation of 1 H NMR relaxometry data and assignment of signal components to C-S-H interlayer water have become clearer over recent years, although previous work attempting to --- ---- KW.JIJllf a c..atCt~ottblndii'JC1TI6J m-m 1~-: -P------~: ·---~-lO-M--~~; ~~~. --------~----, • · ·- 1 2 "ll : : i·- r,_ Shon : :·- ll T First EdTo !·- Flrtt Edto . . . : I~ "-' Mnllile'~*-ila~Cif()I{~A}IIOr~l) llJka I Cllrxt.CHa...- 1 WM.01())1011d,kJ ....... 1\War ~·-•hlrAt r,pe&sn ~aiANICiffltrlllli.llraweaf ... lllupi'-JMIIJdwr~~-•.a..,ulmtcM&aatill...,~ lJillllllllr---aftlrdaa t'dlo,ollld 21._., ~oflbellnlldlo lila 11zs betqt«IIIJII'IdtiiD~q!htii!Wnt~tTa4cnlmiiJIJIIDJofdluaf...ulpt&ID. Ver*llcbr.bedlll5thcwdlr ~1 1 ,1!-JJidl, dl.ll* "'dle.,.,...afd!rfT\l,J&'I pcJ"t*"""*4tllldC-~~~~ _j 58