Topics in Cement and Concrete Research

In recent decades, the construction sector has faced many changes. One of these changes is the shift in the role of national government from one-sided practices in which the government was solely responsible for strategic and long-term spatial planning to a multi-actor and multi-level arena. One outcome was a rearrangement of the balance between public and private responsibilities. This has led to new procurement routes and contracts as Private Finance Initiative (PFI) and Public Private Partnerships (PPP), as well as to a more performance-oriented client (both public and private). At the same time, construction firms changed their strategic focus from cost efficiency to adding value for money for the client, resulting in new contract forms such as Design & Construct (D&C), Building, Operate & Transfer (BOT) and variants there from. So far, governments of most European countries have their own restrictive specifications for the use of building materials

Workability-Integrated Mixture Proportioning Method for Pervious Concrete

Portland cement pervious concrete (PCPC) is increasingly gaining attention as a preferred material in selected pavement applications. This concrete has several unique features, which makes it an environment-friendly construction material. Its porous structure allows precipitation to infiltrate directly into the ground. This reduces accumulation of a large amount of storm water in areas of heavy storms and recharges the ground water system, thus reducing the need for expensive storm water collection and treatment systems. Also, it allows the pollutants on pavement surfaces such as motor oil, etc. to drain into the subsurface be treated by native microbes in the soil, rather than be washed off into storm water and pollute the receiving waters. Additionally, due to its high albedo value, PCPC provides cooler pavement surfaces. While pervious concrete has several advantages, there are certain challenges with its production and operations which have hindered its wide-spread use. Lack of adequate mixture-proportioning methods that account for workability is one of the principal challenges. The workability issues in PCPC are related to various factors. Factors such as the open-graded aggregate graduation, the reduction or elimination of fine aggregates, the restriction on paste content and low paste flowability are typical reasons for the poor workability in PCPC, although these are the same features that render the PCPC function as they enhance the porosity in the mix

Distributed Robust Partial State Consensus Control for Chain Interconnected Delay Systems

Partial state consensus (PSC) is investigated for chain interconnected systems with time-varying delays and parameter uncertainties. A novel design philosophy of PSC control is proposed and a sequential calculation method is presented to guarantee the robustness of the controller. A sufficient condition based on linear matrix inequalities (LMIs) is derived and the stability is proven by the Lyapunov method. The proposed approach can ensure that the states which are subject to a consensus constraint achieve consensus, while those without a consensus constraint track their own set points. Finally, numerical simulations and a solution proportioning experiment are developed to validate the effectiveness of the proposed method

A hierarchical adaptive nonlinear model predictive control approach for maximizing tire force usage in autonomous vehicles

The ability to reliably maximize tire force usage would improve the safety of autonomous vehicles, especially in challenging edge cases. However, vehicle control near the limits of handling has many challenges, including robustly contending with tire force saturation, balancing model fidelity and computational efficiency, and coordinating inputs with the lower level chassis control system. This work studies Nonlinear Model Predictive Control for limit handling, specifically adapting to changing tire-road conditions and maximally allocating tire force utilization. We present a novel hierarchical framework that combines a single-track model with longitudinal weight transfer dynamics in the predictive control layer, with lateral brake distribution occurring at the chassis control layer. This vehicle model is simultaneously used in an Unscented Kalman Filter for online friction estimation. Comparative experiments on a full-scale vehicle operating on a race track at up to 95% of maximum tire force usage demonstrate the overall practical effectiveness of this approach.Comment: Preprint of accepted paper in Field Robotic

COMPARISON BETWEEN MODEL PREDICTIVE CONTROL AND PID CONTROL FOR WATER-LEVEL MAINTENANCE IN A TWO-TANK SYSTEM

The objective of this study is to investigate the Model predictive control (MPC) strategy, analyze and compare the control effects with Proportional-Integral-Derivative (PID) control strategy in maintaining a water level system. An advanced control method, MPC has been widely used and well received in a wide variety of applications in process control, it utilizes an explicit process model to predict the future response of a process and solve an optimal control problem with a finite horizon at each sampling instant. In this thesis, we first designed and built up a closed-loop two-tank water level system. Next, we modeled the system and linearized the model for simplification in the analysis and design. Then, we implemented the model in a simulation environment based on Matlab. We tried both MPC and PID control methods to design the controller for the two-tank system, and compared the results in terms of settling time, overshoot, and steady-state error under various operational conditions including time delays. The results showed the advantage of MPC for dealing with the system dynamic over PID and could be designed for more complex and fast system dynamics even in presence of constraints

Control of clogging in permeable concrete pavements

This thesis aims to improve the understanding of clogging and the effects this has on permeable concrete, and to develop new permeable concretes that are more durable and resistant to clogging without the need for frequent maintenance. Permeable concrete, also known as pervious concrete, is used to reduce urban flooding as it allows water to flow through normally impermeable infrastructure. It is prone to clogging by particulate matter and predicting the long-term performance of permeable concrete is challenging as there is currently no reliable means of characterising clogging potential. New methods were developed to study clogging and define clogging potential. The tests involved applying flowing water containing sand and/or clay in cycles, and measuring the change in permeability. Three methods were used to define clogging potential based on measuring the initial permeability decay, half-life cycle and number of cycles to full clogging. We show for the first time strong linear correlations between these parameters for a wide range of samples, indicating their use for service-life prediction. The problem which leads to clogging in existing permeable concrete is the pore network that is highly tortuous, with variable cross-section and random interconnectivity. As a result, it is important to develop new permeable concretes that have uniform pore structures with tortuosity of 1. This thesis reports on the development of cementitious materials that can be poured on-site, or provided as pre-cast elements, forming a low tortuosity connected porosity microstructure so that surface water is effectively transferred from one side of the permeable pavement to the other, with minimal risk of clogging. High-strength clogging resistant permeable pavement (CRP) was prepared by introducing direct channels of varying size and number into self-compacting mortar. In all cases, permeability and compressive strength proved to be far higher than conventional permeable concrete. More significantly, not a single sample became clogged despite extensive cyclic exposure to flow containing sand and/or clay. We show for the first time a high strength clogging resistant permeable pavement capable of retaining sufficient porosity and permeability for storm-water infiltration throughout the service life while having a high compressive strength to utilise permeable pavement in heavy loading applications. This innovative system will help alleviate urban flooding and contribute towards a more sustainable urbanisation. In order for the new design to be considered a truly successful innovation it is necessary to examine means by which the work done in a laboratory setting can be utilised in a large-scale commercial setting. Several methods have been investigated. While each of these methods has benefits and limitations, collectively they constitute a valid range of possible approaches for potential in-situ and pre-cast delivery of CRPs on a large scale.Open Acces

Toward salt-scaling resistant concrete

The main objective of this research study was to (1) improve the understanding of the underlying mechanisms of durability-related deterioration in pavements; (2) improve the understanding of methods for extending pavement life, i.e., mixture ingredients; and (3) implement tools and specifications that will increase the longevity of concrete pavements. To this end, since it was of special interest to enhance current knowledge regarding salt-scaling resistance of concrete, an extensive effort was made in conducting a comprehensive literature review on the topic, after which an experimental program was designed to study the (i) relationship between the air-void system and salt scaling, (ii) effect of mixture components on hardened concrete properties and salt-scaling potential, (iii) impact of workmanship, i.e., effects of different finishing times and curing regimes on the scaling resistance of the concrete specimens, and (iv) correlation between concretes’ hardened properties and salt-scaling resistance. Statistical univariate and multivariable regression models were developed for use by researchers and field engineers, using non-destructive tests, i.e., ultrasonic pulse velocity (UPV) and rebound hammer (RH), to facilitate the prediction of concretes’ hardened properties and salt-scaling resistance. Ultimately, the contributions of each of the investigated factors on concretes’ hardened properties and salt scaling resistance were statistically investigated and corresponding multivariate-regression models were developed. The collection of mixture variables included water-to-cementitious materials (w/cm) ratio, paste volume, slag cement, and air content. Concrete performance was mainly investigated through tests of abrasion resistance, sorptivity, compressive strength, and salt scaling. Shrinkage and freeze-thaw resistance of the concrete mixtures were also tested to evaluate the effects of paste volume on concrete’s hardened properties. Finally, research continues toward assessing the correlation between cement chemistry and salt-scaling damage