Dynamic Modulus of Elasticity of Some Mortars Prepared from Selected Jordanian Masonry Cements

In light of the highly demanding cement market in Jordan, comprehensive studies should be undertaken to investigate the properties of the different cement types. This paper studies the Dynamic modulus of elasticity (DME) at 2, 7 and 28 days in mortars using six cement Jordanian types with CaO con-tents less than that of the ordinary Portland cements. It was found that the DME has strong relation with compressive strength. At the age of 28 days the mortars had some different values of DME. One important result of our work is that DME at the age of 28 days can be derived from those of the two days mixes. To account for the differences in dynamic modulus of elasticity with time, it is highly recommended to study in detail the mortars petrography under the light microscope. Using the scanning electron microscope (SEM), usually with attachment for chemical analysis at the crystal scale, in addition to X-ray diffraction technique may help characterization of the cement phases qualitatively and quantitatively.


Introduction
Mortars, used mostly in masonry construction, are similar to concrete mixes but without the coarse aggregate fraction with sand-cement ratio are usually around 3. Cements used for masonry purposes are being produced by partial replacement of OPC with pozzolan and/or lime materials as in [1] [2] [3] [4], and [5]. Reference [6] investigated the utilization of volcanic scoria from "Djoungo" (Cameroon) as cement and fine aggregate replacement in Portland How to cite this paper: Al-Baijat, H.  9, 199-206. cement masonry mortar. The study was carried out on two groups of mortars samples, mortars containing NPs as cement replacement by 25% and 45% by mass (OPC/NPs mortars) and mortars containing VSA as sand substitution at level of 25%, 50%, 75% and 100% by mass (VS mortars). Flow value, fresh and dry density, dynamic modulus and mechanical strengths of mortars at 28, 56 and 90 days were evaluated. Based on the results, they found that adding "Djoungo" volcanic scoria as cement replacement or by sand substitution in the appropriate ratio in mortar can be applicable for masonry. Reference [7] studied the prospect of recycling dredged sediments in self-compacting mortars (SCM) and their impact on the fresh and hardened properties of SCC pastes/mortars. Fifteen mortars/paste mixes were prepared using the response surface methodology. The responses were the workability and fluidity of the self-compacting pastes, and the mechanical properties of the self-compacting mortars (compressive, bending strength, and dynamic modulus of elasticity). A numerical optimization was used to select the optimal mixture with the maximum amount of treated sediments while maintaining self-compactibility properties. Thus, cement pastes or mortars made with such cements would have better strength and durability properties than those made with conventional cements. Very limited studies were performed to study the performance of these pastes in Jordan. Reference [8] has studied different aspects of a masonry cement produced by the Jordanian Cement Manufacturing Company (Lafarge). In a previous paper [9], we discussed the compressive strength of cements. Here, we are going to study the dynamic modulus of elasticity DME of the previously mentioned six cement brands.

Methodology
Two kg of each cement type were used by the senior author to prepare the different mixes and conduct the following tests: fineness, consistency or flow, and compressive strength (for details see [9]), according [10]  Dynamic modulus of elasticity, was measured by using ultrasonic measurement device to measure the speed rate in the concrete specimen. The following formula was used to determine the modulus:  Table 1 of [9] summarizes the results of the physical properties and compressive strength and Table 2 measurements on propagation time of longitudinal ultrasonic waves from which values of the dynamic modulus of elasticity calculated. Figure 1 shows the dynamic moduli of elasticity for the studied mortar types at 2, 7, and 28 day ages. At the age of 28 days the highest dynamic modulus of elasticity was recorded by Rasikh and the lowest by Shamaliyya cements. Table 3 shows how the dynamic modulus increases with time. Figure 2 shows that the 28 day modulus can be predicted from that of the 2 day modulus with a correlation coefficient exceeding 0.9.

Conclusions and Recommendations
The following conclusions can be drawn out from the present work: 1) There are some variations in the dynamic modulus of elasticity between the different brands of mortars prepared from the six Jordanian cements.            2) The 28 day dynamic modulus of elasticity of mortars can be derived from 2 day modulus.
3) An inverse linear relationship exists between dynamic modulus of elasticity and water absorption. As the cements used here have less CaO content than standard OPC cements, their cement mineral phases cannot be derived by Bogue equation. Microscopy (SEM) and X-ray diffraction may be used to identify the type and amount of cement mineral phases. Poisson ratio was assumed to be 0.17 in the present work. It is highly recommended to measure the actual Poisson ratio and repeat this work including more cement types and mixes with different water cement ratios.

Conflicts of Interest
The author declares no conflicts of interest regarding the publication of this paper.