The reaction of blast furnace slag in sodium hydroxide (NaOH) solutions of different molarities is evaluated. The compressive strength of the activated slag does not scale with the molarity of NaOH. The primary reaction product in the activated slag is identified with calcium aluminosilicate hydrate [C(A)SH]. While the early reactivity of slag is enhanced at higher alkalinity, and the dissolution of slag increases with the molarity of NaOH, the quantity of C(A)SH in the hydrating system does not scale with the molarity of NaOH in the activated slag. From X-ray diffraction (XRD) analysis, an additional water-soluble, sodium-based amorphous product is identified in the reaction products. The water-soluble product, which does not contribute to strength, increases proportionately with the initial Na content in the solution. At higher molarity, there is a larger proportion of the water-soluble product relative to C(A)SH in the reaction products. The $\mathrm{Ca}/\mathrm{Si}$ ratio and $\mathrm{Al}/\mathrm{Si}$ ratios in the C(A)SH gel are relatively invariant of the NaOH molarity in the activating solution. The compressive strength gain in the alkali-activated slag is determined by the quantities of C(A)SH and the intrinsic sodium-filled water-soluble product.

An experimental investigation on the fracture test response of notched concrete beams with two types of discrete macrosynthetic fibres is presented. The influence of high-modulus polypropylene macro fibres on crack propagation and opening was evaluated using the digital image correlation technique. The surface displacements measured close to the tip of the notch were analysed to evaluate the crack opening profile in concrete in relation to the observed load response. A method for precisely estimating the displacement discontinuity across the crack from measured surface displacements was developed. Post-peak softening in the flexural load response was found to be associated with crack advance in the cementitious matrix. The measured crack opening profiles in the post-cracking response indicated a hinge-type behaviour in the beam. The physical hinge in the post-cracking flexural response of the beam was directly determined from the surface measurements. It was found that the addition of macrosynthetic fibres up to 8 kg/m³ (0·9% by volume) did not significantly influence crack propagation but provided resistance to opening of the hinge, which resulted in an increase in toughness and significant load recovery in the post-peak flexural load response.

An X-ray diffraction (XRD)-based evaluation of the crystalline and amorphous phases in slag hydrating in an alkaline environment is presented. A method is developed for the quantification of the amorphous phases present in hydrating slag in a sodium hydroxide solution. In hydrating slag, the amorphous reaction product is identified as calcium aluminosilicate hydrate. A water-soluble sodium-based amorphous reaction product is also produced. The XRD-based quantification method relies on the direct decomposition of the XRD intensity pattern of the total amorphous phase present in partially hydrated slag into the intensity patterns of the amorphous unreacted slag, the hydrate and the sodium-based product. The unreacted slag content in partially hydrated slag is also determined from the decomposition of the intensity signature of the total amorphous phase. An independent verification of the amorphous unreacted slag content in hydrating slag is obtained from measurements of blends of unhydrated and partially hydrated slag. The XRD-based phase-quantification procedure developed here provides a basis for evaluating the extent of reaction in hydrating slag.