Construction of pavements layers on subgrade with excellent to good properties reduces the thickness of the layers and consequently reduces the initial and maintenance cost of highways and vice versa. However, construction of pavements on poor subgrade is unavoidable due to several constrains. Improvement of subgrade properties using traditional additives such as lime and Portland cement adds supplementary costs. Therefore, using by-products in this domain involves technical, economic, and environmental advantages. Cement kiln dust (CKD) is generated in huge quantities as a by-product material in Portland cement plants. Therefore, it can be considered as an excellent alternative in this domain. In Iraq, Portland cement plants generate about 350000 tons of CKD annually which is available for free. Therefore, Iraq can be adopted as a case study. This paper covers using CKD to improve the properties of poor subgrade soils based on series of California Bearing Ration (CBR) tests on sets of untreated samples and samples treated with different doses of CKD in combination with different curing periods to investigate their effects on soil properties. The results exhibited that adding 20% of CKD with curing for 14 days increases the CBR value from 3.4% for untreated soil to 48% for treated soil; it, also, decreases the swelling ratio. To determine the effects of using this dose under the mentioned curing period on the designed thicknesses of pavements layers, a case study was adopted. The case study results exhibited that treatment of the subgrade soil by 20% of CKD with curing for 14 days reduces the cost of the pavements by $25.875 per square meter

Constructing highway pavements faces complex problems, which are affected by multiple factors, where solution is nearly impossible without expert assistance. Diagnosing such construction problems and suggesting most suitable cost efficient solutions requires significant engineering expertise, which might not be available in all construction sites due to inadequate resource and remote locations. Developing an expert system in this domain is a very effective way to help novice engineers to overcome these problems and to learn about them. Moreover, the system can be used as an archive to document engineering knowledge and to share expertise among the experts in this domain. This article describes the development and evaluation stages of such a system, including knowledge acquisition, knowledge representation, system building, and system verification and validation. The initial knowledge is acquired from literature reviews. More expert knowledge is elicited through interviews and questionnaires. This knowledge is documented, analyzed, represented, and converted to computer software using the Visual Basic programming language and the system is called ES-CCPRHP. The system has been verified and validated in three ways: by extensive testing, comparison between system performance and expert reasoning, and case study. It can therefore be employed with confidence by end users.

Imperfections of plastic concrete can cause severe deteriorations in rigid pavements surface and structure and reduce its life and serviceability. Diagnosing these imperfections, identifying their causes, and applying effective remedies early can prevent costly repairs in rigid pavements. However, if these imperfections are not remedied in correct time, the deteriorations in rigid pavements shall be reminded as soon as possible to avoid worsening the pavement condition. This domain involves diagnostic nature which suitable to be modelled as an expert system to help practicing engineers to identify the causes of the problems and their expected effects on pavement as well as applying suitable remedies. This paper presents the stages of development of an expert system in this domain. The development process includes knowledge elicitation, knowledge representation, knowledge coding, system validation, verification and evaluation.