The research paper presents an analysis of autogenous shrinkage development in self-consolidating concrete (SCC). The first stage of the study involved an evaluation of concrete susceptibility to cracking caused by shrinkage of SCC with natural and lightweight aggregate. The shrinkage was tested on concrete rings according to ASTM C 1581/C 1581M- 09a. The influence of aggregate composition, the water content in lightweight aggregate, and SRA admixture on the reduction of concrete susceptibility to cracking, due to the early-age shrinkage deformation was determined. In the second stage of the research, the innovative method measurement of autogenous shrinkage was developed and implemented. The tests were performed on concrete block samples, dimensions 35x150x1150 mm, that had the same concrete volume as ring specimen in the ASTM method. Linear deformation of the concrete samples was measured in constant periods of 500 s using dial gauges with digital data loggers. The investigation allowed evaluating of the influence of water/cement (w/c) ratio of 0.28, 0.34, 0.42, and of aggregate composition on the development of autogenous shrinkage in different stages of curing SCC. The results were compared to existing material models proposed by other researchers. The conducted study indicated a significant influence of the w/c ratio and composition of aggregate on the concrete susceptibility to crack caused by the autogenous shrinkage deformation.

This paper describes the development in concrete technology for offshore concrete structures from the 1970’s until now and discusses some potential topics for future research which would result in more cost-effective offshore concrete structures.

Most of the offshore concrete structures constructed in the last 4 decades are still in operation, with no or only minor maintenance required, even though the average age for these structures in the North Sea is more than 25 years. The compressive strength in offshore structures has gradually increased from about 40MPa (5800 psi) in the 1970’s to more than 100MPa (14500 psi) in some of the latest concrete structures. Standards and concrete specifications have been revised several times during these years. In parallel, the knowledge from several research and development programs has been used to further improve the concrete properties and overcome the limitations. Focus has been primarily to improve the compressive strength of the concrete as well as the durability and concrete workability. The cement and admixture industry have been heavily involved in research programs to further adapt and develop these material properties. The result of the product developments in the concrete constituency has also improved cost-effectiveness and durability (including overall life-cycle cost-effectiveness) for offshore concrete structures.

With the new generation technology, the technical limitations we face today will be overcome. With more knowledge and improved technology, the quantity and size of cracks in concrete in service are expected to be reduced, which would also improve durability. In addition, the focus in the future will also be on sustainable and environmentally friendly materials.

In this study, we tested compressive strength, rheology, initial setting time and transport properties of mortar samples mixed with green corrosion-inhibiting admixtures were tested. Four types of green corrosion inhibitors were adopted, which were extracted from peony leave, Kentucky blue grass, sugar beet leave and dandelion. All of them affected the compressive strength adversely but improved other properties of mortar samples. Resistance of mortar to chloride induced corrosion was evaluated using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) techniques. The results indicated that these green corrosion-inhibiting admixtures provided promising inhibiting performance under chloride environment. The results also suggested these green corrosion-inhibitors have the potential to be used as multifunction corrosion inhibitors for concrete, such as serving as water reducer and set retarder. Future work would focus on chemical mechanism of green corrosion inhibitors and the comparative evaluation of these green corrosion inhibitors with other commercially available corrosion inhibitors.

The durability of alkali activated concrete (AAC) synthesized using high calcium fly ashes (FAs) was studied. Surface resistivity, bulk electrical resistivity, rapid chloride ions penetration, and freeze-thaw resistance tests were carried out on AAC made with five different FAs. The specimens were either oven-or moist-cured. The effect of adding air entraining admixture (AEA) and recycled crumb rubber to the AAC specimens on the freeze-thaw resistance was investigated as well. It was found that the durability of AAC was higher than that of comparable ordinary Portland cement (OPC) concrete. Adding the AEA improved the freeze-thaw resistance but not enough to complete the 300 cycles, per ASTM C666-15. Adding the rubber to the AAC mixtures improved the freeze-thaw resistance significantly.

Statistics show an increase in the use of fly ash in concrete to improve both sustainability and performance. However, concrete incorporating high volume fly ash has encountered an issue with incompatibility between fly ash and air entraining admixture (AEA). This study investigates using ground recycled rubber (GRR) as an eco-friendly alternative to AEA to improve the freeze-thaw performance of mortar mixtures incorporating two different types and ratios of fly ash. Two different sizes and ratios of GRR were used in this study. The results were compared with mixtures having two different types and dosages of AEA as well as a reference mortar mixture having neither GRR nor AEA. Foam indices were determined for both types of fly ash and compared with cement. The compressive strength retention values of mortar cubes after exposing them to 36 freeze-thaw cycles were determined and linked to the air content of each mixture. This study revealed that the GRR outperformed the AEA in terms of the freeze-thaw durability where all mixtures retained their compressive strengths. However, the performance of mixtures including AEA was inconsistent depending on the chemical composition of the fly ash, fly ash replacement ratio, and AEA dosage.