# Nuclear Magnetic Resonance in Tire Waste Mortars
## 2 Materials and Methods  
The mortar mixtures were prepared using CEM I 42.5 R cement, natural hydraulic lime (NHL 3.5 or NHL 5) (EN 459-1) [26], standardized silica sand (EN 196-1) [27], potable tap water, food-grade casein powder, commercial latex emulsion (SBR type), and recycled SBR rubber flakes [28; 29; 30; 31], (1-3 mm, no surface pretreatment). Mix proportions were expressed as percentages relative to the cement mass, and a w/b ratio of 0.50 was maintained. Samples were cast in 40 mm \(\times\) 40 mm \(\times\) 160 mmolds, demolded after 24 h, and cured in a humidity chamber (20 \({}^{\circ}\)C, RH \(>\) 95%). Mechanical tests followed EN 196-1 and EN 1015 series standards [32]. For NMR analysis, samples were broken into 5-8 mm fragments to fit into 18 mm diameter tubes, with approximately 10 g of material per sample. Samples were conditioned at room temperature (20 \(\pm\) 2 \({}^{\circ}\)C) for 24 h prior to analysis. NMR tests used a Bruker Minispec MQ20 (Bruker, Billerica, MA, USA) at 20 MHz with CPMG sequence (100 \(\upmu\)s echo time, 1024 echoes, 64 averages). T\({}_{2}\) relaxation times were determined using CONTIN 3.0 with regularization parameter \(\lambda\) = 0.01. To reduce noise interference, thresholding was applied based on a 5% signal-to-noise ratio. Measurements were performed on three samples per formulation, and average values were reported. The persistent T\({}_{2}\) peak around 30-40 ms observed at 28 days is attributed to contributions from \({}^{1}\)H nuclei in organic compounds such as casein and rubber additives, which do not fully integrate into the cement matrix. Additionally, the experimental program also incorporated more advanced research methods, which we aim to highlight in this article. Specifically, Nuclear Magnetic Resonance (NMR) tests were conducted. Exceptional samples and results obtained from the construction materials laboratory were subjected to further advanced testing to explain the time-dependent behavior of the newly developed materials and their performance compared to the reference mixture. Also, the transverse relaxation measurements were conducted using the widely recognized Carr-Purcell-Meiboom-Gill (CPMG) method. The below figure illustrates the radiofrequency pulse sequence, and the corresponding echo train obtained during the experiment. A key benefit of this multiple-echo approach is its rapid acquisition, enabling repeated signal averaging--a crucial factor in enhancing detection sensitivity, particularly in low-field experiments. When the CPMG decay curve (Figure 2) follows a mono-exponentialtrend and diffusion effects are negligible over the intervals *s*, the transverse relaxation time (T\({}_{2}\)) of the sample can be determined by fitting the data to the Equation (1):  
\[A_{n}=A_{0}e^{-\frac{2\pi\tau}{T_{2}}} \tag{1}\]  
where \(A_{n}\) is the amplitude of the \(n\)-th echo, \(A_{0}\) is a constant depending on magnetization and filling factor, \(\tau\) is the time between echoes, and \(T_{2}\) is the transverse relaxation time. To assess potential diffusion effects on echo decay, experiments with varying echo times can be performed. However, if the relaxation time varies across the sample due to heterogeneity or differences in surface relaxivity--as often occurs in liquids confined within porous mortars--the CPMG decay curve is expected to exhibit a multi-exponential behavior. Here's the graph of the CPMG (Figure 3) pulse sequence showing the initial 90\({}^{\circ}\) pulse in the blue spike, followed by a series of 180\({}^{\circ}\) pulses, illustrated in the red dashed spikes, appearing at regular intervals, decreasing in amplitude to mimic T\({}_{2}\) relaxation. Figure 3: Echo Amplitude Decay in CPMG Sequence. Figure 2: CPMG pulse sequence showing the initial 90\({}^{\circ}\) and 180\({}^{\circ}\) pulses. technique does not destroy the samples. Thus, this innovative technique is non-destructive and completely non-invasive. The most well-known application of Nuclear Magnetic Resonance is undoubtedly in medicine, where it is known.