Mechanical properties of ready mix mortar: evolution with time and degree of hydration

Abstract The aim of the present study was to evaluate the properties of fresh and hardened state and the hydration degree of ready mix mortar at different ages. The mortars were produced with the same water/ dry materials ratio (13%), same content of air-entrained admixtures (0.35% of cement mass), while three contents of hydration stabilising admixtures (0%, 0.4% and 0.8%) were evaluated. The ready mix mortars were characterised in two storage times (0 and 48 hours) in the fresh state through the consistency index, specific gravity, air entrained content, water retention, setting time and rheological parameters. In the hardened state, the mortars were evaluated at 7, 14, 28, 42 and 56 days for: compressive strength, tensile strength, specific gravity and elasticity modulus. The hydration degree was also evaluated by three methods: ignition loss, thermogravimetric analysis and X-ray diffraction. The results demonstrate that the content of hydration stabilising admixture influences the properties of the mortars. The degree of hydration was influenced by the hydration stabilising admixture over time. However, it was not possible to correlate degree of hydration with compressive strength, which was influenced also by others factors.

摘要 本研究旨在评估不同龄期预拌砂浆（ready mix mortar）的新拌与硬化状态性能及水化程度。本次试验制备的砂浆采用相同的水/干料比（13%）、相同的引气外加剂（air-entrained admixtures）掺量（占水泥质量的0.35%），并设置了3种水化稳定外加剂（hydration stabilising admixtures）掺量（0%、0.4%和0.8%）开展对比测试。针对新拌状态的预拌砂浆，分别在0小时和48小时两种存储时长下，通过稠度指数、表观密度、含气量、保水性、凝结时间及流变参数对其进行性能表征。对于硬化状态的砂浆，则在7、14、28、42和56天龄期时，分别测试其抗压强度、抗拉强度、表观密度与弹性模量。此外，本研究还通过烧失量法、热重分析法及X射线衍射（X-ray diffraction）三种方法评估砂浆的水化程度。研究结果表明，水化稳定外加剂的掺量会对砂浆的各项性能产生影响；水化程度随养护时间的变化也会受到水化稳定外加剂的调控。然而，无法将水化程度与抗压强度建立关联，因为抗压强度同时还受到其他多种因素的影响。