Steel-Concrete Bond in High-Strength Lightweight Concrete.
High-strength, lightweight aggregate concrete has many uses for specialized applications such as marine structures, pilings, and earthquake considerations. These examples use this concrete to reduce dead loads. Lightweight aggregate (LWA) concrete has a lower unit weight and modulus of elasticity causing an advantage over conventional concrete. LWA concrete also saves on transportation, form work, concrete placement, and plant maintenance since it is substantially lighter than normal weight concrete. However, present codes assume inferior bond properties based on splitting in tensile strength of the concrete (ACI 318).
The most important reasons for using LWA concrete are improved durability, fatigue resistance, and a unit weight in air that is 75 to 80 percent comparable to NWA concrete. Submerged in water, the LWA concrete's weight is only 60 percent of the unit weight of NWA concrete. Lower thermal conductivity and thermal expansion contribute enhanced resistance to thermal cracking while making the material a better insulator. .
Steel-concrete bonds are the combinations of adhesion, friction, and the support of the ribs in deformed steel. The adhesion mechanism is the first property activated by the load. Both friction and rib supports are put into action when the adhesion property fails and some movement begins between the steel and the concrete. At this point, the reinforced concrete should not slip, causing serious deformation and possible internal cracking. The test performed defines maximum desired bond slip in LWA concrete.
To study the bond and strength properties of lightweight aggregate concrete; the test compares two aggregates (LWA and NWA) and one mineral admixture, condensed silica fume. The strength of both aggregates were achieved by either a very low water ratio or by using the admixture. An ASTM Type I/II low-alkali portland cement was used.