An experimental study of some mechanical properties and absorption for polymer-modi ﬁ ed cement mortar modi ﬁ ed with superplasticizer

: Polymer-modi ﬁ ed concrete and mortars are widely used with di ﬀ erent purposes in precast concrete and pre-stressed concrete structural elements, bridge decks, buildings, and repair requirements because of their signi ﬁ cant behavior under di ﬀ erent conditions, such as durability against freezing and thawing, ability to absorb impact loads and good mechanical properties compared to ordinary concretes. This study aims to improve some mechanical properties of cement mortar by using styrene – butadiene rubber (SBR) latex, a superplasticizer, and also decreasing the absorption level to lower values by using these two admix-tures. The study shows that using 10% SBR by weight of cement increases the compressive strength from 28.6 to 30.8 MPa and decreases the absorption from 2.3 to 1.7% which gives durability for cement mortar. This study also shows the development in strength achieved by using SBR superplasticizer simultaneously, and absorption decreases to only 0.76% for 10% SBR mixes. In comparison, it was 1.75% for mixes with SBR only.


Introduction
Polymer-modified concrete (PMC) and polymer-modified mortars (PMM) are concrete types with polymers added as admixtures.Various percentages of polymers were added relative to the weight of cement.Polymer concrete, PMC, and mortar applications are not new.during the 1970s, polymer-modified cement composites were used in the United Kingdom and some other countries, but are now used widely all over the world.The benefit of using polymers such as styrene-butadiene rubber (SBR) and other liquid polymers is to improve the quality of concrete and mechanical properties of concrete such as compressive, flexural, and tensile strength, it also improves freezing and thawing effects [1,2].The impact strength or impact resistance can be highly improved by using polymers in concrete.Polymer concrete can be used in precast and prestressed concrete systems, overlays, repair work, maintenance, and concrete bridge decks [3,4].Less absorption or less permeable concrete can also be achieved using polymer concrete, which is a more durable than ordinary concrete [5][6][7][8], superplasticizer and polymers are used widely to improve the properties of concrete and durability [9,10].
Polymer-modified cement mortar had been investigated and improved with silica fume powder by Gao [11] to achieve higher values in mechanical properties.The effect of polymers on ultra-high performance concrete was studied by Mayhoub [12] and he concluded that using polymers in ultra-high strength concrete improve mechanical properties and durability in later stages.Polymers are also used in carbon fiber polymer bars to improve the properties of concrete [13].This study aims to improve some of the properties of PMM used in superplasticizers.This study also includes mechanical properties such as compressive strength, tensile strength, and absorption.fine aggregates used were yellow sand.Its sieve analysis is shown in Table 1 and confirms zone 2 according to Indian Standards Limits [14].
The polymer used in the study is white SBR, and is used as 0, 5, 10, and 15% of the weight of cement.
The superplasticizer used is from type PC-200 and is used to improve the properties of polymer-modified cement mortar.It is used as a 1% cement weight.

Laboratory tests
Cubes of specimens were used for each mix to calculate the absorption of PMM.After 28 days of curing in water, the specimens were weighed to calculate the average saturated weight (W2).The specimens were then dried in the oven for 24 h to calculate the dry weight (W1).The absorption rate calculated using the following equation: where W1 is the dry weight of the concrete specimen and, W2 is the saturated weight of the concrete specimen.Additionally, the compressive strength of three specimens for each mix were tested, and taking the average value, and tensile strength was tried by using 100 × 200 mm cylinders and tested for splitting tensile test (indirect method); the tensile strength value of the specimen was calculated using the following equation: where σt is the tensile strength of a concrete cylinder, P is the max load from the machine (until failure), D is the diameter of the cylinder, and L is the length (or height) of the cylinder.
Figure 1 shows the cubic specimen under the compression test, and also shows the cylindrical concrete specimen under the tensile test (splitting test).Figure 2 shows few specimens after the compression test.

Results and discussion
Table 2 shows the absorption, compressive strength, and tensile strength of PMM and reference mix (without polymers) properties.From this table, PMM with 10% SBR polymer gives the best results and less absorption than other mixes, and this mix can be considered as the optimum mix.The reference mix shows 28.6 MPa in compressive strength while the 10% P/C mix gives 30.8 MPa.Absorption decreased from 2.3 to 1.75%, giving concrete more durability.The 15% ratio shows lesser mechanical property values and slightly lower absorption.Table 3 shows the same mixes but modified with superplasticizer mechanical properties improved by using superplasticizer.Less absorption was achieved compared to Table 1.
Figures 3-5 show the relation between polymer/cement ratio and compressive strength, tensile strength, and absorption of PMM with the reference mix.The compressive strength increased by increasing the SBR polymer dosage to 10%, but then it slightly decreased, as shown in Figure 3.The tensile strength increased by increasing the polymer/ cement ratio to 10% dosage, but absorption decreased beyond 10%, as shown in Figure 5.
Using a superplasticizer improves the mechanical properties of PMM, as shown in Figures 6 and 7.The results show a higher increment in compressive and tensile strength compared to ordinary PMM, but less absorption was obtained by using superplasticizers as shown in Figure 8.The following outcomes can be pointed out: 1. Polymer-modified cement mortar can be improved using a superplasticizer with higher compressive and tensile strength than ordinary polymer-modified mortar.2. Using 10% SBR by weight of cement increases the compressive strength from 28.6 to 30.8 MPa and decreases absorption from 2.3 to 1.7%.
3. Significantly lower values in absorption were achieved in the study using a superplasticizer.The absorption lowered to only 0.76%, while in ordinary polymer mortar it was 1.75%, making polymer-modified cement mortar long-lasting.

Recommendations and further studies
• Owing to the large diversity of concrete types, we advise employing polymers in reactive powder concrete or high performance concrete.These polymers reduce permeability and absorption, making the concrete more durable.• We advise performing parametric studies with additional elements and additions using numerical analysis (finite element approach).• Using field models to validate the outcomes of the experiments carried out for this study.
Funding information: Authors state no funding involved.
Author contributions: All authors have accepted the responsibility for the entire content of this manuscript and consented to its submission to the journal, reviewed all the results and approved the final version of the manuscript.QAJ and ZSA designed the experiments and AHJ carried them out.HSH developed the model code and performed the simulations.QAJ prepared the manuscript with contributions from all co-authors.
Conflict of interest: Authors state no conflict of interest.
Data availability statement: Most datasets generated and analyzed in this study are in this submitted manuscript.The other datasets are available on reasonable request from the corresponding author with the attached information.

Figure 1 :
Figure 1: Tensile and compression tests for PMM specimens.

Figure 3 :
Figure 3: Relationship between polymer/cement ratio and compressive strength of PMM.

Figure 4 :
Figure 4: Relationship between polymer/cement ratio and tensile strength of PMM.

Figure 8 :
Figure 8: Relationship between polymer/cement ratio and absorption of PMM using superplasticizer.

Figure 7 :
Figure 7: Relationship between polymer/cement ratio and tensile strength of PMM using superplasticizer.

Table 1 :
Sieve analysis for sand confirming with zone 2 limits

Table 2 :
Some properties of PMM with reference mix

Table 3 :
Some properties of PMM were modified with a superplasticizer with a reference mix