2.1. Cement

CEM II B/L – 32.5 N cement was used as this is the most commonly used in masonry mortars fabrication binder. UNE-EN 197-1: 2011 standard (24) and the RC-08 cement receipt instruction (25) the properties of this type of binders. Their characteristics are shown in Table 1.

2.2. Aggregates

To fabricate the reference mixes NA provided by Cemex company were used. Recycled mortars were elaborated using three different types of RA: concrete RA, mixed RA and ceramic RA coming from integral waste treatment plants “Molar”, “Salmedina” and “Tec-Rec” respectively situated in the Community of Madrid. The aggregates were sieved in the laboratory in order to eliminate fine fraction due to its poorer properties, until obtaining a fine fraction of aggregates passing through 4mm sieve and retained in 0.063 mm sieve (4/0.063 mm).

2.3. Additive

Because of high absorption of RA compared with NA, recycled mortars were elaborated using Glenium Sky 604 additive to obtain a plastic consistency without incrementing the excess of mix water. The additive was provided and prescribed by the technical department of BASF Company.

2.4. Insulating

To separate floor sheets and to study the impact of interposition of acoustic insulator under different geometries between two surfaces, elastic supports of expanded polystyrene (EPS) of low density (10 kg/dm³) were designed using software FreeCAD 0.16 (26). Afterwards and due to its difficult manual execution, it was decided to automate cutting process through numeric control. These insulators are evenly distributed over the entire inferior surface of sheets, producing in this way an effect of floatability that mitigates impacts provoked by hitting upper side of slabs. Characteristics of different geometries of EPS used in this research are shown in Table 2 and can be observed in Figure 1.

Figura 1. Insulating EPS supports of different geometries.

3.1. Dosages

Experimental program was developed using CEM II/B-L 32.5 N binder. To elaborate recycled mortars three percentages of substitution of NA were used: 50%, 75% y 100%, of each one of three types of used RA, with a relation 1:4 between both compounds (cement to aggregate in conditions of dry weight).

Fabrication of each of the mixes was performed using planetary mixer of CIB-701model of Ibertest brand, following the recommendation of the UNE-EN 196-1 standard (27). The amount of water used for mortars elaboration was needed to obtain plastic consistency according to the standard UNE-EN 1015-3 (28), that is to say, runoff value of 175±10 mm. Mixes fabricated with RA contained 1% of additive over the weight of cement.

The description of mortars used in the tests is performed following the nomenclature:

M – A – T – X

where M indicates that this is cement mortar, A is the type of aggregate that can be NA in case of NA or RA in case of RA, T is the type of RA, that can be C for concrete RA, M in case of mixed RA and Ce in case of ceramic RA. Finally, X indicates the percentage of substitution of RA 50%, 75% or 100%. Table 3 shows the dosages used in this research.

3.2. Experimental program

Experimental program was divided into three parts. The first part was dedicated to the characterization of different aggregates used for mortars elaboration. During the second part the tests of bulk and real density, compactness and flexural strength were performed for different mortar mixes elaborated with both natural and RA. In order to determine the existence or no existence of significant differences in the behaviour of mortars made with different percentages of substitution of RA, a statistical analysis using ANOVA table was performed. For all the ANOVA performed in this research it was verified that the residuals complies with three conditions: independence, normality and homoscedasticity. The design of experiment carried out in this part of research is based on the factors and levels shown in Table 4.

Finally, once the results were analyzed, those dosages that after statistical study presented significant improvement were chosen to carry out the test of impact noise and to study the influence of the composition of mortar and the geometry of insulators on the speed of propagation of vibrations through the elaborated sheets.

As it can be seen in Figure 2, unlike the standardized equipment proposed by the UNE-EN ISO 10140-5:2011 standard (29), this research used an alternative equipment based on a round-shaped metallic level hammer with 15 mm radius and a sphericity over 500 mm, that allow obtaining the unique even impact in all the tests in the way that the energy introduced into the system was always the same.

Figura 2. Measuring equipment.

Transducer able to measure vibrations produced in buildings was used to perform the measurements. It is formed by the triaxial accelerometer CESVA© able to detect impacts of very low frequency, and by the vibrometer of VC431 model that allows obtaining in real time a response in terms of speed of propagation of vibration. Moreover, it can be connected to a computer in order to save the collected data of taken measures.

4.1. Characterization of aggregates

Characterization of aggregates used in this research was performed following the requirements established by the UNE-EN 13139 (30) standard. Tests of physical characterization give the following results shown in Table 5.

As it can be seen in Table 5 main characteristics of RA compared to NA are lower density, higher friability coefficient, and higher water absorption. These characteristics are crucial both for physical characteristics of mortars and their mechanic behaviour and are caused mainly by the amount of adhered mortar in RA as found in other researches (31),(32).

In terms of relative and bulk density, RA of ceramic and mixed type are those which present significantly lower value compared to concrete RA, as it can be seen in multiple range test shown in Tables 6 and 7.

In terms of chemical requirements which RA have to comply with to be used in mortar fabrication, chlorides and sulphurs content tests were carried out following the UNE-EN 1744-1 (33) standard. As it can be observed in Table 8, the content of chlorides soluble in water does not overcome the limit established by the standard UNE-EN 998-2 (34) of 0.06%. Furthermore, the content of total sulphur never overcomes the limit if 1% established by the standard UNE-EN 13139 (30).

According to the obtained results, three types of RA used in the research comply with the requirements established by the reference standards for their use as a raw material in masonry mortar elaboration.

4.2. Physical properties of mortars

Firstly, the tests of bulk density, real density and compactness of mortar fabricated according to the standard UNE-EN 1015-10 (35) were carried out. The results are shown in Table 9.

Generally, bulk and real density in hardened state are lower in RA compared to the reference mortars. When the amount of used RA increases, both densities decrease and the compactness obtained as quotient between both decreases. This decreases mechanical properties of recycled mortars due to their high porosity.

According to the statistical analysis (Tables 10 and 11) it can be seen that type of used RA and substitution percentage are significant factors having < 0.05 p-value in bulk and real density. Due to the fact that factor of the substitution percentage is significant, it can be concluded that recycled mortars elaborated with 100% of any type of RA have significantly lower bulk and real density than mortars elaborated with different substitution percentage.

In terms of multiple range tests, both in case of dry density and real density, there are no significant differences between mortars made with concrete RA and mixed RA. However, mixes elaborated with ceramic RA show significantly lower density. As an example, Table 12 shows multiple range test for bulk density.

To complete the characterization of RA and to evaluate other properties of mortars which have influence on the speed of propagation, flexural strength test was carried out. The results are shown in Figure 3.

Figura 3. Flexural strength test for different aggregates and substitution rates.

For all the used dosages the decrease of flexural strength was observed when the amount of used RA increases, observing important decreases in mixes with 100% of RA as was expected. Comparing flexural strength of recycled mortars with one of mortars made with natural sand (4.36 MPa), the loss of flexural strength between 16% and 30% was observed depending on the quantity and the type of incorporated recycled aggregates.

ANOVA table for “flexural strength” variable shows that both factors are important and consequently have influence on this property. In multiple range tests it can be seen that there are significant differences only between the mixes made with concrete RA and mixes elaborated with other types of RA (Table 13).

After analyzing the results of the characterization of cement mortars, the test of impact vibrations transmission was carried out only for the mixes that incorporate 100% of three types of RA because of their significantly lower density as shown in performed ANOVA table.

4.3. Impact vibrations transmission

Transmission of impact vibrations produced by the hitting equipment over the surface of elaborated sheets and quantified in terms of speed of propagation is shown in Table 14, where are shown the results obtained measuring each of four corners of sheets, using or not four geometries of EPS insulation in order to determine the influence on the impact mitigation (Figure 4).

Figura 4. Measuring equipment.

To analyze the results of this part of the research, ANOVA table was performed. The factors were the type of RA used for mortar elaboration and four types of insulation described in section 2.4. In case of RA the corresponding levels of this factor are: NA, RA-C, RA-M and RA-Ce and in case of insulation types there are five levels: insulation 1(A), insulation 2 (B), insulation 3(C), insulation 4(D) and without insulation (NI). The results of ANOVA table are shown in Table 15.

As it can be seen in Table 15, both factors taken into consideration are important for the proposed variable “propagation speed” as its p-value is less than 0.05. Another multiple range test was also carried out to determine at which levels there are differences within the analyzed factors (Tables 16 and 17).

Observing Table 16 it can be concluded that there are significant differences in terms of propagation speed, and in case of RA propagation speed is lower. Among different types of RA significant differences were obtained, being concrete RA one that presents the highest propagation speed compared to mixed and ceramic RA between which no significant differences were observed.

Regarding the type of insulating, Table 17 shows that the use of insulation in mortar sheets reduces significantly the propagation speed through the material. Analyzing different insulations, four different homogenous groups were observed, where insulation of type D presents better behavior compared to others types.

Vibrometer VC431 described in part 3.2 was used to obtain the levels of acoustic insulation of the mortars in dB using different types of insulation. The results are shown in Table 18.

Therefore, both the use of RA in the elaboration of mortars and the incorporation of insulation into the material improve the behaviour towards impact noise, as they decrease significantly the propagation speed of wave through the material. The mortars elaborated with 100% of mixed and ceramic RA in combination with type D insulation are studied typologies that have a better behaviour towards impact noise, reducing to 20% the speed of propagation through the material with regard to mortars fabricated with natural aggregates, which means an improvement of insulation of 20 dB as can be seen in Table 18.