The development of the Strength Index Method and protocol for assessing the use of solid waste materials in concrete

In the United States, each person generates about three to four pounds of urban solid waste each day. Landfilling is the most frequently used disposal method. One method of disposing solid wastes is to use it in concrete. Solid wastes are currently being used in concrete. However, a review of literature indicates that there is no general methodology for assessing the use of solid waste in concrete. The protocol was developed by determining the critical issues of using an SWM in concrete. The critical issues include the SWM background, chemical and physical properties, and reactivity, and the effect the SWM has on concrete properties, the environment, and its cost. Four wastewater sludge ashes from different wastewater treatment plants were used to test the protocol. The sludge ashes were from St. Louis, Missouri (Bissel Point and Lemay), and Cedar Rapids and Dubuque, Iowa. The chemical properties showed that the sludge ashes are primarily silicon dioxide when determined by x-ray fluorescence, x-ray diffraction and energy dispersive x-ray. The physical analysis of the sludge ashes showed that the sludge ashes are best suited for use as a cement replacement instead of an aggregate replacement. The reactive nature of the solid waste material was determined by the development of the Strength Index Method (SIM). The SIM was based on the reactivity of known solid waste materials that are currently being used in concrete.; The reactivity of the sludge ashes, as measured by the SIM showed that the sludge ashes in this study can be classified as reactive using the 28 day index values. Concrete containing sludge ash generally exhibited less compressive strength and modulus of elasticity when compared to concrete containing 100% portland cement (control) at all test ages. The stress-strain relationship for the BP and CR concretes were not as stiff as the control concrete but DU and LM concretes exhibited equivalent stiffness as the control concrete. All concrete specimens exceeded the minimum freeze-thaw requirements for durable concrete as tested under ASTM C 666. Concrete mixes containing sludge ash passed the toxicity leaching test and provide economic benefits to the producer and user.