Auto Identification of Rolling Layers in Roller-Compacted Concrete Dam

A scheme for identifying rolling layers in roller-compacted concrete (RCC) dam automatically was presented. First, a conceptual model was developed. Second, by using a computational geometry method, the auto identification of rolling layers and auto matching between rolling compaction machines and rolling layers were realized based on spatial control points. An application to the construction of Guandi RCC dam showed that the auto identification of rolling layers played an important role in ensuring the engineering quality.

Relationship between compressive and tensile strengths of roller-compacted concrete

The abstract roller-compacted concrete （RCC） is a zero slump concrete comprising the same materials as that of conventional concrete with different proportions. The RCC must be compacted to reach its final form. The effects of hydration and aggregate interlock on its strength are considerable. For similar binder contents, the compressive strength of the RCC is generally higher than that of the conventional concrete; however, the tensile strength of RCC may not be superior to that of the conventional concrete. Adequate tensile strength is necessary to resist fatigue cracking, particularly in pavement applications. However, the compressive strength is frequently used in assessing the quality control and quality assurance of pavements. Therefore, the relationship between the compressive and tensile strengths of the RCC should be analyzed. Unfortunately, only a few studies have been conducted on this relationship. The objective of this study is to identify the difference between the indirect tensile strengths of the RCC and those of the conventional concrete as well as develop relationship equations to evaluate the compressive and tensile strengths. In this study, regression equations are developed to estimate the indirect tensile strengths, which are known as flexural and splitting tensile strengths, using the compressive strength of the RCC. The results show that the flexural strength of the RCC is within the predicted values obtained from the conventional concrete equations for a given compressive strength. In contrast, the splitting tensile strength of the RCC is relatively lower than that of the conventional concrete for the given compressive strength.

Evaluation of early-age strains and stresses in roller-compacted concrete pavement

In the structural design of a roller-compacted concrete pavement(RCCP), it is crucial to estimate strain and stress developments in the RCCP slab realistically. Since the RCCP mix uses less cement and lower amount of water, shrinkage strain and concrete temperature during the hardening stage are expected to be reduced as compared to those of conventional concrete mixture, resulting in a reduction of the concrete early-age deformation and stress developments in the RCCP slab. In this paper, early-age concrete strain and stress developments in RCCP slab subjected to environmental loads were evaluated. A full-scale test section of RCCP under real climatic conditions was monitored. The early-age total strains,stress-independent strains, shrinkage strains, and coefficient of thermal expansion(CTE) of the RCCP were measured and analyzed. Using the results of measured strains, in-situ CTE and shrinkage strain, and temperature, the early-age concrete stress development is computed by incorporating a viscoelastic property of the early-age concrete. The results revealed that the shrinkage strain of the RCCP is quite low as compared to that of conventional concrete. The early-age stress developments in the RCCP slab are strongly governed by the thermal-induced stresses. Shrinkage-induced stresses were quite small and might be negligible in a preliminary estimation of early-age stress developments in the RCCP slab.

Calculation Model of Equivalent Strength for Induced Crack Based on Double-K Fracture Theory and Its Optimizing Setting in RCC Arch Dam

By means of fracture testing on roller-compacted concrete （RCC） three-point bending beams with two different specimen sizes, the P-CMOD complete curve for RCC was gained. Furthermore, by applying double-K fracture theory, KiniⅠC,KunⅠC, as well as the critical effective crack length and the critical crack tip opening displacement, were evaluated. Based on the double-K fracture parameters above, the calculation model of equivalent strength for induced crack was established, thus the calculation method on its initiation, stable propagation and unstable fracture was ascertained. Moreover, the finite element simulation analysis of stress field in ShaPai arch dam and the on-site observational splaying points of induced crack at different altitudes validated the reliability of the model. Finally, crack inducer′s optimal setting in RCC arch dam was studied. It improves the design level of induced crack in RCC arch dam and satisfies the necessity of engineering practice.

智能化振动压路机动力学建模及参数优化

为了能够使智能化振动压路机在不同的压实阶段下进行最有效的压实作业，通过建立连耦工况下“振动轮一土体”四自由度动力学模型，分析得到了不同工作参数与振动轮及机架位移之间的关系，采用计算得到的模拟参数进行优化，得到了压实度最大且不引起跳振时的激振频率和激振角度，为振动压路机在各压实阶段下参数的优选提供数值依据。数据表明：随着土体状况的变化，压路机的激振频率保持在土体2阶固有频率的1．29—1．39倍范围内作业时．土体压实度达到最大值。

智能化振动压路机振动参数动态分析

为了更加精确地分析振动压路机的压实过程,建立了考虑土体随动质量的智能化振动压路机连耦工况下的六自由度系统动力学模型,并将其应用于某型智能化振动压路机的动态分析。对该振动压路机的设计参数进行优化,获得了该振动压路机的最优工作参数,从而实现了对智能化振动压路机振动压实过程的有效控制,提高了压实过程中的密实度和压实效率,改善了整机的舒适性。