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ACI 318, “Structural Concrete Building Code,” has been completely reorganized for the 2014 edition. While the technical provisions of most of the code have been unchanged, changes have been made in the provisions dealing with responsibility, durability, and construction. The responsibility for use of the code has been assigned to the licensed design professional (LDP.) Minor changes have been made to the durability provisions to clarify the intent of the code and to help the LDP select exposure classes. The most significant changes in ACI 318-2014 are in a new chapter that addresses construction requirements. Previously, construction provisions were located throughout the code. The new code is based upon the premise that the contractor should not have to search the code for construction requirements. Instead, all such requirements must be in the construction documents that are a part of the contract between the owner and the contractor. The new chapter makes the LDP responsible for writing the applicable design information and compliance requirements into the construction documents.

Materials for grouting post-tensioning tendons of a bridge at below freezing temperature (–10oC or 14oF) were studied. The water/cementitious material ratio was a maximum of 0.32 and the grout properties were tested at -10oC (14oF) according to applicable Chinese standards for past-tensioning grouts. After special treatment, the efflux times of the modified grouts were between 14 and 22 seconds after mixing and less than 30 seconds after 60 minutes without agitation. The final strength of the grout reached 50-60 MPa (7975-8700 psi) after 35 days of curing (7 days at below freezing temperature and 28 days at a standard temperature), which was 95%-100% of the reference strength for curing at a standard temperature.

Calcium sulfoaluminate (CSA) cements, composed by binary (CSA clinker-anhydrite) and ternary (CSA clinker-Portland cement-anhydrite) mixtures with C S/CAS43 molar ratios ranging from 1.9 to 5.0 and Portland cement concentrations comprised between 40% and 70% by mass, were investigated. They were paste-hydrated (w/c mass ratio, 0.5), cured from 4 hours to 28 days and submitted to differential thermal-thermogravimetric (DTA-TG) and X-ray diffraction (XRD) analyses as well as mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Expansion of paste specimens cured under water and compressive strength on cement mortars were also determined. Relatively high values of (i) C S/CAS43 ratio and solution alkalinity, and (ii) ettringite concentration in the cementitious matrix promoted expansion and compressive strength development, respectively. The formation of expansive ettringite was associated with peculiar SEM and MIP features such as thin [from less than 0.1 µm (0.000004 in) to about 0.3 µm (0.000012 in)] ettringite crystals and pore size distributions shifted toward higher radii, when compared to those related to non-expansive cements.

Early compressive strength development in sprayed concrete is a crucial factor for success. A full scale mixing and spraying test have been done in Mapei’s Shotcrete Test Centre (STC) in Norway. Two identical batches of fresh concrete have been made, but with +13 °C (55.4 °F) and +28 °C (82.4 °F) fresh concrete temperature. Two sample boxes from each concrete batch have been sprayed with 9% alkali-free accelerator and have been stored in warm +20 °C (68 °F) and cold +5 °C (41 °F) conditions. A higher temperature in fresh concrete increased the compressive strength the first hour, while warmer conditions when curing had a stronger influence on the compressive strength at 6, 12 and 24 hour.

Ternary cement composites consisting of metakaolin sand (MKS), natural clayey diatomite (CD) and calcined clayey diatomite (CCD) with various reciprocal combinations up to 15 wt. % and water-cementitious materials ratio of 0.5 were studied. Phase composition and strength of one-year old composites cured in water at (68 ± 33.8) °F [(20 ± 1) °C] were compared with reference portland cement (PC) paste. Compressive strengths of ternary cement composites on (MKS + CD) and (MKS + CCD) bases exhibited notable similarity and were slightly higher than those of reference paste. Pozzolanic reaction resulting in portlandite consumption and sustained formations of calciumsilicate (CSH) and calciumaluminate (CAH) hydrates was confirmed in the studied composites. Micropore and total pore median radii were reduced opposite to those observed in reference paste. Calcination of natural CD towards CCD formation was found redundant because of the considerably similar character of CD and CCD effect on the formed phase composition and strength uptakes.