A combination of experimental tests and numerical models of mortarless structures is needed because numerical models that are validated against experimental data can be used to explore further a wide range of untested scenarios. This combination is essential to assess, optimize, and better understand mortarless masonry systems—as has been discussed, at length throughout this literature review. Relevant studies from past years have combined the experimental tests and numerical modeling (brought up above) to make extraordinary progress in the availability of information on mortared and mortarless masonry; however, there is significant room for advancements in the coming years, such as:
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(1) Dry-stack masonry has several advantages over mortared masonry, including a reduction in construction time, costs, and the amount of wet materials needed. The common methods to compensate for the lack of mortar in masonry systems include: using non-interlocking and interlocking units that can be grouted and reinforced. Other alternatives that enhance structural performance can include adding surface bonding agents and using pre-stressed reinforcement elements. The dry-stack construction system presents a myriad of design opportunities with essentially infinite variations in the interlocking units, surface treatment and reinforcement abilities. This new design configuration requires further investigation and improved methods to predict the structural behavior of these masonry systems. Previous research shows that such design variations can cause significant changes in the behavior of the system. Hence, a more thorough understanding of the effect and sensitivity of various design decisions on mortarless masonry systems is needed. Several variables should be explored, including: (i) the change in the coefficient of friction in the presence of simultaneous vertical and lateral loads; (ii) the aspect ratios of walls; (iii) the effects of various percentages of reinforcement and grouting; (iv) the effects of different thicknesses of surface bonding; and (iv) the effects of various types of interlocking units.
(2) Only a limited number of studies have considered the effect of the variability of the unit material. Several material properties that exhibit natural variability should be explored with probabilistic models. This study can include a detail study of the surface roughness and the microscopic distribution of the asperities in the bed surfaces area of the units.
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(3) Future studies are needed to develop mitigation strategies for reducing contact surface irregularities between units. For instance, dry-stack masonry prisms tend to have relatively higher initial deformations when subjected to vertical loads of up to approximately 30% of the failure load of prisms. This can result in stiffness in the response at low levels of applied loads. Dry-stack masonry prisms exhibit stable compressive behavior after the units are settled because, when loading is increased, the contact area at the interface is greater. This increases the stiffness of the prism. One potential solution to this is to ground the bed surfaces to reduce roughness and eliminate the large deformations that result from the crushing of the rough surface. Future studies are needed to investigate this concept and its potentially negative effect on the shear capacity of the system due to the reduced coefficient of friction between the units. (4) Dry-stack systems have been tested with a thin layer of mortar between units, which
tends to have a minor impact on masonry performance. Instead of a thin layer of mortar, an alternative strategy is the application of low-cost, easy-to-lay (e.g., sprayable, spreadable with a foam gun) bonding material between units. Studies on such materials must include tests to determine the mechanical properties of these bonding materials. (5) Multiple studies show that the efficiency factor of dry-stack masonry systems can be
represented by the ratio of the compressive strength of a masonry prism to the compressive strength of a single unit. For mortared masonry systems, the maximum efficiency factor has been found to be approximately 0.98. This review found that the average efficiency factor was approximately 0.65 for non-interlocking systems and ranged from 0.20 to 0.92 for interlocking systems depending on the type of unit.
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However, for surface bonding and pre-stressed reinforcement elements, the information is unavailable in the available literature.
(6) Dry-stacked masonry systems need to be studied under different geometric configurations to include one- and two-way behavior of walls. It also needs to be studied when looking at the “one- and two-way behavior of windows and door openings from within the wall. Moreover, research on the shear capacity of dry-stack masonry remains inconclusive because of the complex behavior of the friction contact between units during the loading process. Dynamic loads on mortarless masonry walls need to be studied to assess their behavior in high-seismic zones.
(7) Recent studies have shown that pre-stressed dry-stack masonry systems can withstand vertical, in-plane, and out-of-plane loads. However, the capacity of the systems relies on the kind of surface contact between units. Uneven contact between units creates instabilities during the pre-stressing process, leading to a reduced load capacity. In addition, researchers have found that typical equations in building codes are not applicable to pre-stressed dry-stack masonry systems. Efforts towards the adjustments of those equations are needed for design purposes.
(8) Additional research is needed in a wide range of design configurations to determine the compressive, shear, and flexural capacities of dry-stack masonry systems so that researchers can establish design guidelines for the practical use of such systems.