Rheology of Cement Mortars with Crushed Fine Aggregates of Different Lithological Types

Crushed fine aggregates are widely used for full or partial replacement of natural sands in concretes. The crushed sands present different characteristics from the natural sand, especially if taking into account the content of microfine particle, the distribution of particle sizes, the shape features, besides the different lithological origin. From the rheological point of view, the crushed sands frequently provide mixtures with high yield stress, high viscosity, high cohesion and internal friction, which hinders its use in concrete. This study is focused on the evaluation of the rheological behavior of concrete mortar phase when using different lithological types of crushed sand in total replacement of natural sand. The lithological types surveyed were granite, calcitic limestone, dolomite limestone and mica schist. Each of these sand types was studied in two ways： in natura and with adjusted grading curve. The results show the best performance of calcitic limestone providing lower viscosities and lower yield stress in mortars.

The Permeability and Strength of Green High Performance Concrete

The permeability,alkali silica reaction,workability and strength of GHPC(green high performance concrete) were studied in this paper.The results show that GHPC has an excellent durability and the effects of mass ratio of flyash to high calcium slag,water binder ratio,content of water reducer,and crushed coarse aggregate type on the workability and strength of GHPC were considerably evident.A new path for the concretes continuous development was put forward.

Laboratory evaluation of cement treated aggregate containing crushed clay brick

The waste clay bricks from debris of buildings were evaluated through lab tests as environ- mental friendly materials for pavement sub-base in the research. Five sets of coarse aggregates which contained 0, 25%, 50%, 75% and 100% crushed bricks, respectively, were blended with sand and treated by 5 % cement. The test results indicated that cement treated aggregate which contains crushed clay brick aggregate had a lower maximum dry density （MDD） and a higher optimum moisture content （OMC）. Moreover, the unconfined compressive strength （UCS）, resilience modulus, splitting strength, and frost resistance performance of the specimens decreased with increase of the amount of crushed clay brick aggregate. On the other hand, it can be observed that the use of crushed clay brick in the mixture decreased the dry shrinkage strain of the specimens. Compared with the asphalt pave- ment design specifications of China, the results imply that the substitution rate of natural aggregate with crushed clay brick aggregate in the cement treated aggregate sub-base material should be less than 50% （5 % cement content in the mixture）. Furthermore, it needs to be noted that the cement treated aggre- gate which contains crushed clay bricks should be cautiously used in the cold region due to its insuffi- cient frost resistance performance.

Fresh and hardened properties of high-strength concrete incorporating byproduct fine crushed aggregate as partial replacement of natural sand

This paper presents the fresh and hardened properties of high-strength concrete comprising byproduct fine crushed aggregates(FCAs)sourced from the crushing of three different types of rocks,namely granophyre,basalt,and granite.The lowest void contents of the combined fine aggregates were observed when 40%to 60%of natural sand is replaced by the FCAs.By the replacement of 40%FCAs,the slump and bleeding of concrete with a water-to-cement ratio of 0.45 decreased by approximately 15%and 50%,respectively,owing to the relatively high fines content of the FCAs.The 28 d compressive strength of concrete was 50 MPa when 40%FCAs were used.The slight decrease in tensile strength from the FCAs is attributed to the flakiness of the particles.The correlations between the splitting tensile and compressive strengths of normal concrete provided in the AS 3600 and ACI 318 design standards are applicable for concrete using the FCAs as partial replacement of sand.The maximum 56 d drying shrinkage is 520 microstrains,which is significantly less than the recommended limit of 1000 microstrains by AS 3600 for concrete.Therefore,the use of these byproduct FCAs can be considered as a sustainable alternative option for the production of high-strength green concrete.