# Aggregate Type and Concrete Age Effects on Anchor Breakout Performance: Large Database and Insights
## 5 Conclusions  
An experimental campaign performed by two different research groups is presented with the aim to investigate a potential effect of aggregate type and concrete age on the load capacity for anchors loaded in tension and shear. The experimental investigation involves anchors installed in seven low- and four high-strength concretes tested at two different ages. The tests on anchors under tensile loading were carried out on headed studs, while shear tests were performed on headed studs and bonded anchors. Based on the experimentally obtained data sets and systematically carried out analysis, the following conclusions are drawn. Experimentally obtained concrete cone capacities are compared to the current empirical model in terms of concrete compressive strength. Results clearly show that the current empirical model underestimates experimental values by around 20-30% for the first tested age (28 days) for the studied anchor type and geometry. Relative concrete cone capacities in tension reveal practically minor differences among all tested concretes. The effect of different petrography of the coarse aggregates used in this study is shown to be smaller than the typically expected scatter in this type of structural test. Results show a relative difference between normalized values of ~7% in the case of the 28-day tests. Therefore, it can be concluded that the current empirical model captures sufficiently well the effect of different aggregates. The analysis of anchor capacities in tension, normalized by the compressive strength determined at the respective age, reveals a systematic increase in conservatism with age for almost all investigated concretes. Based on the mean value for all investigated concretes, predictions at the second age are about 9% higher with a scatter band of approximately 15%. In the case of anchors under shear loading, similar trends are observed. Differences in coarse aggregate type seem to be reasonably well captured by the current model based on concrete compressive strength. Experimental mean values agree well with the model predictions. While the normalized values scatter more compared to the tensile tests, the scatter between concretes remains smaller than the scatter within individual test series. Figure 9: Ratio between relative shear load capacities for all different concretes and aggregates. Also, in the case of concrete edge breakout, an aging trend is found, leading to more conservative results at later ages. Even though the mean of all shear prediction ratios is equal to 1.06, for some concretes a more pronounced aging effect is observed than for others (up to 20%). Further studies comprising structural anchor tests for concretes with different cement types and ideally more ages are necessary to confirm the findings and to develop a more systematic understanding of aging effects on anchor performance. Such future studies should also consider different anchor types and variations in the geometry of the problem (e.g., embedment depth, head size, edge distance, etc.) [41]. For both considered failure modes, the analysis shows that the L.A. coefficient is unsuitable to describe the effect of coarse aggregate type on either concrete properties, concrete cone capacity in tension, or concrete edge breakout in shear. Analyses of concrete cone and half-cone shapes by size measurements (CSTB) or advanced photogrammetric analysis (CDL) showed minor differences related to the coarse aggregate type or age [27; 32]. [PERSON] and [PERSON] conceived and designed the \"CDL\" experiments. [PERSON] and [PERSON] conceived and designed the \"CSTB\" experiments. Conceptualization, [PERSON] and [PERSON]; methodology, K.N. and [PERSON], writing--original draft preparation, K.N., with contributions from [PERSON]; writing--review and editing, K.N., [PERSON] and O.A.M. ; supervision, [PERSON]. All authors have read and agreed to the published version of the manuscript. This research was funded by the Christian Doppler Forschungsgesellschaft, Grant LICROFAST to [PERSON].