Experimental Study On Anchorage Properties Of Anchors Grouted By Micro-expansive Geopolymer Mortar

Grouting material is the key medium for anchorage to transmit anchoring force.Cement mortar commonly used as grouting material is easy to shrink and crack,which may lead to anchor corrosion or failure.In addition,the production of Portland cement is regarded as an important factor of greenhouse effect and air pollution.Geopolymer is environmentally friendly.It has small drying shrinkage,high resistance for acid and alkali,and comparatively stronger weak alkaline than cement,which can form better anticorrosion protection for anchorage.This thesis is aimed to investigate the feasibility of using geopolymer as anchorage grouting material.The main research contents and results of this thesis are as follows:1.Flexural strength,compressive strength and bond strength of geopolymer mortar,geopolymer paste and cement mortar are tested respectively,and basic mechanical performance of the three materials were compared.Based on the results,pull-out tests were conducted on 28 grouted anchors and the influence of anchor type,anchoring space,grout type and anchorage length were explored.The test results showed that:(1)Compared to cement mortar with similar compressive strength,geopolymer mortar has higher bond strength with anchor.For screw anchor with diameter of 16 mm,an embedded depth of 8d(where d referred to the diameter of anchor)was deep enough to make anchor yield in pullout tests,and a depth of 12 d can make anchor fracture when using geopolymer mortar and geopolymer paste as grout.When using cement mortar as grout,an embedded depth of 10 d was required for anchor yielding,but a depth of 12 d cannot ensure the anchor fracture.(2)When using geopolymer mortar and geopolymer paste as grout,a minimum embedded depth of 12 d was recommended for screw anchor.2.Tests on compressive strength and vertical expansion(shrinkage)rate of geopolymer mortar with different proportion(0%,7%,8%)of expansive agent were carried out,and the results were compared to that of cement mortar.Then the bond strength between grouting material and concrete substrate was tested by push-out tests,and micro-structure at the interface between grouting material and concrete substrate was analyzed using SEM.From the test results,the following conclusions can be derived:(1)Adding expansive aget slowed the development of early strength of geopolymer mortar,but the compressive strength of geopolymer mortar with expansive agent at 90-day curing age approached to that of geopolymer mortar without expansive agent.(2)The curing time for developing stable shrinkage and the final shrinkage of geopolymer mortar without expansive agent were both lower than that of cement mortar,while geopolymer mortar with expansive agent would produce proper expansion.(3)At 28-day curing age,bond strength between concrete substrate and geopolymer mortar with 7% of expansive agent was 1.3 times and 2 times higher than that of geopolymer mortar without expansive agent and cement mortar with similar compressive strength.(3)the bonding interface between the micro expansive geopolymer mortar and aggregates(or cement mortar)in concrete substrate was so dense that fewer cracks and holes can be seen,while cracks can be found at the interface between the new cement mortar and aggregates(or cement mortar)in concrete substrate.3.Pull-out tests were conducted on 50 anchors grouted by four kinds of grouting materials(micro expansive geopolymer mortar with expansive agent proportion of 7% and 8%,nonexpansive geopolymer mortar and cement mortar).The influence of grout type,anchor type,curing time,anchor diameter and anchorage length on bond properties between grout and anchor were investigated.In addition,the distribution of axial stress of the anchor along embedded depth and bond stress between grouting material and anchor were explored.The results showed that:(1)regardless of grouting types,when bond(pull-out)failure occurred,the failure always occurred on the anchor-grout interface,but not at the grout-concrete substrate interface.(2)bond strength between cement mortar and anchor was far lower than that of micro expansive geopolymer mortar with similar compressive strength.(3)along embedded depth,axial stress decreases gradually,while the bond stress is rather a small amout at the pulling end of rockbolt,but it reaches peak value afer a short distance away from the pulling end of rockbolt and then decreases gradually.The bonding force between the grout and the anchor may be weakened with increasing load,and the peak value of bolt bond stress will change the position from the pulling end of rockbolt to deep into the embedded length of rockbolt.Compared to the cement mortar with similar compressive strength,the depth corresponding to the peak value of bond stress between anchor and micro expansive geopolymer mortar was shallower.