International Concrete Abstracts Portal

Sixty percent of the nation's highly toxic and radioactive mixed wastes are stored at Hanford in 177 deteriorating underground storage tanks. To close or remove these storage tanks from service and place them in a condition that is protective of human health and the environment, the tanks must be physically stabilized to prevent subsidence once wastes have been retrieved. Remaining residual liquid waste in the tanks that cannot be removed must be solidified and the solid wastes encapsulated to meet the Nuclear Regulatory Commission, Department of Energy, Environmental Protection Agency, and the State of Washington requirements. The Department of Energy has developed cementitious flowable concretes to restrict access and provide chemical stabilization for radionuclides. Formulation, laboratory, and field testing for application at Hanford began with flowable, self-leveling structural and non-structural fills. A slump flow equal to or greater than 610 mm, 0% bleed water, and 0.1% (by volume) shrinkage measurements were key parameters guiding reformulation efforts that resulted in highly flowable, self-consolidating concretes that met Hanford 241-C Tank closure short- and long-term regulatory and engineering performance requirements.

Repair and strengthening of concrete and masonry structures using fabric-reinforced cementitious matrix (FRCM) and streel-reinforced grout (SRG) are emerging technologies in the industry allowing engineers and contractors to effectively remove deficiencies, improve structural performance and prolong life of existing concrete or masonry structures. FRCM is a composite consisting of one or more layers of cement- or hydraulic-based matrix reinforced with dry fibers in the form of open fabric. Similarly, SRG consists of a matrix reinforced with cords of twisted micro steel wires woven to form a fabric (mesh). Acceptance Criteria AC434 was published to provide guidelines for the evaluation of FRCM/SRG strengthening of concrete and masonry structural elements because the building codes in the USA do not have requirements for testing and determination of structural capacity, reliability and serviceability of this class of composite technologies. AC434 establishes requirements for testing and calculations that can lead to the issuance of a product research reports as evidence of a product’s building code compliance. This paper summarizes and presents the key features of AC434 and its relationship to ACI committee 549.4R, the guide to design and construction of externally bonded FRCM and SRG systems for repair and strengthening concrete and masonry structures.

The use of Externally Bonded Reinforcement (EBR) techniques is widely increasing in the last decades to strengthen both masonry and RC constructions. The use of different EBR configurations is well established also in the refurbishment of historical masonry constructions. The performance of different EBR techniques applied on existing historic masonry vaults was investigated in this work by means of in-situ destructive tests. The brick barrel vaults were located in Castel San Pietro, Verona (Italy) and were 5.6 m span, 1.1 m rise and 27 cm thick. The research focuses on inorganic applications by textiles and lime mortar matrix. In one case by steel reinforce grout and in the other with basalt textile reinforced mortar. Another system was based on common organic matrix. In addition to the experimental results of the static destructive tests of each vault that are discussed in order to evaluate the different response of such applications in terms of strengthening and ductility, a discussion on analytical models regarding the cross section and than the entire vaults are also provided with the aim to define the ultimate load reached by a strengthened vault. Such unique in-field opportunity allowed also some considerations in terms of efficacy and workability of mortar matrices.

ACI’s Certification Department is introducing two new masonry-related certification programs in 2014: the Masonry Field Testing Technician and the Masonry Laboratory Testing Technician. Developed by ACI Subcommittee C601-C, Masonry Testing Technicians (MTT), the programs will be available starting September 1. They will provide certification to those technicians working in the laboratory or in the field who can demonstrate technical knowledge and skills for sampling and testing of masonry units, mortars, grout, and prisms.

I’m trying to resolve an issue on a project with concrete masonry unit (CMU) walls. Although our contract documents specified a compressive strength of masonry (f´m) of 2500 psi (17.2 MPa), the contractor erred and constructed walls assuming an f´m of 1500 psi (10.3 MPa). (While the specified Type S mortar was used, the documentation provided by the CMU producer indicates that the units comply with ASTM C90-12,1 which requires a minimum net area compressive strength of 1900 psi [13.1 MPa], rather than the required 3750 psi [25.9 MPa] unit compressive strength indicated in Table 2 of ACI 530.1.2) The contractor has proposed fully grouting these walls with 3500 psi (24.1 MPa) grout. The proposal includes supporting documentation stating that the combination of 3500 psi (24.1 MPa) grout with 1900 psi (13.1 MPa) units will result in walls with an average compressive strength of 2500 psi (17.2 MPa). The walls were designed as non-load-bearing (flexural loads only) with alternate cells to be grouted and reinforced. ACI 530-112 states that the allowable compressive stress available to resist flexure (Fb) is limited to 0.45f´m. ACI 530.1-112 also states that the grout strength shall equal or exceed f´m when Table 2 of this standard is used. However, it’s my understanding that the compressive strength to be used for strength calculations is the minimum of the masonry units and the grout compressive strengths, which in this case is 1900 psi (13.1 MPa). Can higher- strength grouts be used to compensate for lower-strength CMUs? Are there any testing requirements that I should consider?