PSI - Issue 23

Małgorzata Lenart et al. / Procedia Structural Integrity 23 (2019) 113 – 118 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

114

2

development, Czarnecki, Justnes (2012), Henry et al. (2011), Opon, Henry (2019). The utilization of unused cementitious composites (eg. unused concrete mix) by converting them into granules is part of the principles of sustainable development in the construction. The method developed in recent years, Ferrari et al. (2014), based on the use of a two-component admixture causing caking of cement composites, is used here. The resulting granules can be classified as recycled aggregate and re-used for the production of new cement composites, Lenart , Gruszczyński (2017). The phenomenon of volume changes of cementitious composites is associated in the first phase of cement hydration reactions (including so called chemical shrinkage) and evaporation of water from the surface of the composite (ie. drying shrinkage). Therefore, the composition and properties of the composite itself, Lenart (2015), Rezwani et al. (2019), Wu et al. (2017), Wu et al. (2019), as well as factors related to the ambient conditions in which the cementitious composite is found affect the shrinkage of the composite. The water – cement ratio, the composition and amount of cement, the properties and amount of aggregate can be distinguished in the first group of the factors. The size and amount of ordinary aggregate are an important factor influencing shrinkage. The larger the aggregate grain size, the smaller the cementitious composite shrinkage, Neville (2012), Zhang et al. (2013). However, in the case of lightweight aggregates, their influence on the shrinkage is not unambiguous, Domagała (2014), for example, composites with sintered aggregates exhibit analogous shrinkage as composites made with ordinary aggregates, whereas composites with fly ash hardened aggregate exhibit significant shrinkage. In addition, some of the aggregates themselves exhibit shrinkage. Another important factor influencing the amount of the composite shrinkage is the tested samples size because water evaporates more easily from small samples so the drying shrinkage of such samples is greater. The aim of the conducted research was to determine the influence of the quantity and age of the granules obtained from unused mortar on total shrinkage of newly made mortars. The shrinkage was determined by two methods: the traditional Graff-Kaufmann method carried out on 40 × 40 × 160 mm beams and a modern method of automatic shrinkage measurement carried out in gutters with a width of 100 mm and a measuring length of 1 m. Both methods have their advantages and disadvantages. The Graff-Kaufman method is a relatively cheap one and the beams once made can be stored and examined for a long period of time without causing occupation of the measurement equipment. However, this method does not examine early volume changes. In turn, the automatic method of measuring gutters eliminates the error coming from the manual execution of individual measurements. Moreover, the first measurements of volume changes are made from the moment the fresh mortar is placed in the gutter and what is important, the gutter length is 1 meter that allows direct shrinkage readings in the unit: millimeters per meter. The measurements start at different times (i.e. after about 1 hour in the case of gutters method and after 24 h of the mortar hardening in the case of Graff-Kaufmann method) and that is why the results from both methods are not comparable. The first step in the research program was to make granulate needed for further tests. For this purpose, a granulation admixture consisting of two components: a superabsorbent and a binding accelerator containing calcium aluminate hydrates and sodium silicates was added to the plastic standard mortar (complies with EN 196-1), Ferrari et al. (2013). Each of the components was dosed separately (the first one in the amount of 0.5 kg/m 3 of mortar, the second 6 kg/m 3 ) mixing the mortar for about 2 to 3 minutes each time. The granules thus obtained were scattered for hardening. Because conglomerates were present in the granules after hardening, they were sieved on a sieve of 4 mm (fig.1). One day and 14 days hardening granules were used for further investigations. The granules were matured in the laboratory at 19 o C and 45% humidity. Analyzing the granulate grain size, it can be seen that the maximum graining of the original aggregate (standard sand) was 2 mm whereas the maximum graining of granulate was 16 mm. This is understandable because a part of the grains has been stuck together in the granules whereas there is a coating of the cement grout on the rest grains of sand (fig.2). Detailed analysis of the granulate grain size is presented in Lenart (2018). The moisture content of the 1 2. Research program 2.1. Preparation and properties of granules